drivers/gpu/drm/drm_fb_helper.c

/*
 * Copyright (c) 2006-2009 Red Hat Inc.
 * Copyright (c) 2006-2008 Intel Corporation
 * Copyright (c) 2007 Dave Airlie <airlied@linux.ie>
 *
 * DRM framebuffer helper functions
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 *
 * Authors:
 *      Dave Airlie <airlied@linux.ie>
 *      Jesse Barnes <jesse.barnes@intel.com>
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/console.h>
#include <linux/kernel.h>
#include <linux/sysrq.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <drm/drmP.h>
#include <drm/drm_crtc.h>
#include <drm/drm_fb_helper.h>
#include <drm/drm_crtc_helper.h>
#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>

#include "drm_crtc_helper_internal.h"

static bool drm_fbdev_emulation = true;
module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600);
MODULE_PARM_DESC(fbdev_emulation,
		 "Enable legacy fbdev emulation [default=true]");

static LIST_HEAD(kernel_fb_helper_list);

/**
 * DOC: fbdev helpers
 *
 * The fb helper functions are useful to provide an fbdev on top of a drm kernel
 * mode setting driver. They can be used mostly independently from the crtc
 * helper functions used by many drivers to implement the kernel mode setting
 * interfaces.
 *
 * Initialization is done as a four-step process with drm_fb_helper_prepare(),
 * drm_fb_helper_init(), drm_fb_helper_single_add_all_connectors() and
 * drm_fb_helper_initial_config(). Drivers with fancier requirements than the
 * default behaviour can override the third step with their own code.
 * Teardown is done with drm_fb_helper_fini().
 *
 * At runtime drivers should restore the fbdev console by calling
 * drm_fb_helper_restore_fbdev_mode_unlocked() from their ->lastclose callback.
 * They should also notify the fb helper code from updates to the output
 * configuration by calling drm_fb_helper_hotplug_event(). For easier
 * integration with the output polling code in drm_crtc_helper.c the modeset
 * code provides a ->output_poll_changed callback.
 *
 * All other functions exported by the fb helper library can be used to
 * implement the fbdev driver interface by the driver.
 *
 * It is possible, though perhaps somewhat tricky, to implement race-free
 * hotplug detection using the fbdev helpers. The drm_fb_helper_prepare()
 * helper must be called first to initialize the minimum required to make
 * hotplug detection work. Drivers also need to make sure to properly set up
 * the dev->mode_config.funcs member. After calling drm_kms_helper_poll_init()
 * it is safe to enable interrupts and start processing hotplug events. At the
 * same time, drivers should initialize all modeset objects such as CRTCs,
 * encoders and connectors. To finish up the fbdev helper initialization, the
 * drm_fb_helper_init() function is called. To probe for all attached displays
 * and set up an initial configuration using the detected hardware, drivers
 * should call drm_fb_helper_single_add_all_connectors() followed by
 * drm_fb_helper_initial_config().
 *
 * If &drm_framebuffer_funcs ->dirty is set, the
 * drm_fb_helper_{cfb,sys}_{write,fillrect,copyarea,imageblit} functions will
 * accumulate changes and schedule &drm_fb_helper ->dirty_work to run right
 * away. This worker then calls the dirty() function ensuring that it will
 * always run in process context since the fb_*() function could be running in
 * atomic context. If drm_fb_helper_deferred_io() is used as the deferred_io
 * callback it will also schedule dirty_work with the damage collected from the
 * mmap page writes.
 */

/**
 * drm_fb_helper_single_add_all_connectors() - add all connectors to fbdev
 * 					       emulation helper
 * @fb_helper: fbdev initialized with drm_fb_helper_init
 *
 * This functions adds all the available connectors for use with the given
 * fb_helper. This is a separate step to allow drivers to freely assign
 * connectors to the fbdev, e.g. if some are reserved for special purposes or
 * not adequate to be used for the fbcon.
 *
 * This function is protected against concurrent connector hotadds/removals
 * using drm_fb_helper_add_one_connector() and
 * drm_fb_helper_remove_one_connector().
 */
int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	struct drm_connector *connector;
	int i, ret;

	if (!drm_fbdev_emulation)
		return 0;

	mutex_lock(&dev->mode_config.mutex);
	drm_for_each_connector(connector, dev) {
		ret = drm_fb_helper_add_one_connector(fb_helper, connector);

		if (ret)
			goto fail;
	}
	mutex_unlock(&dev->mode_config.mutex);
	return 0;
fail:
	for (i = 0; i < fb_helper->connector_count; i++) {
		struct drm_fb_helper_connector *fb_helper_connector =
			fb_helper->connector_info[i];

		drm_connector_unreference(fb_helper_connector->connector);

		kfree(fb_helper_connector);
		fb_helper->connector_info[i] = NULL;
	}
	fb_helper->connector_count = 0;
	mutex_unlock(&dev->mode_config.mutex);

	return ret;
}
EXPORT_SYMBOL(drm_fb_helper_single_add_all_connectors);

int drm_fb_helper_add_one_connector(struct drm_fb_helper *fb_helper, struct drm_connector *connector)
{
	struct drm_fb_helper_connector **temp;
	struct drm_fb_helper_connector *fb_helper_connector;

	if (!drm_fbdev_emulation)
		return 0;

	WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));
	if (fb_helper->connector_count + 1 > fb_helper->connector_info_alloc_count) {
		temp = krealloc(fb_helper->connector_info, sizeof(struct drm_fb_helper_connector *) * (fb_helper->connector_count + 1), GFP_KERNEL);
		if (!temp)
			return -ENOMEM;

		fb_helper->connector_info_alloc_count = fb_helper->connector_count + 1;
		fb_helper->connector_info = temp;
	}


	fb_helper_connector = kzalloc(sizeof(struct drm_fb_helper_connector), GFP_KERNEL);
	if (!fb_helper_connector)
		return -ENOMEM;

	drm_connector_reference(connector);
	fb_helper_connector->connector = connector;
	fb_helper->connector_info[fb_helper->connector_count++] = fb_helper_connector;
	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_add_one_connector);

int drm_fb_helper_remove_one_connector(struct drm_fb_helper *fb_helper,
				       struct drm_connector *connector)
{
	struct drm_fb_helper_connector *fb_helper_connector;
	int i, j;

	if (!drm_fbdev_emulation)
		return 0;

	WARN_ON(!mutex_is_locked(&fb_helper->dev->mode_config.mutex));

	for (i = 0; i < fb_helper->connector_count; i++) {
		if (fb_helper->connector_info[i]->connector == connector)
			break;
	}

	if (i == fb_helper->connector_count)
		return -EINVAL;
	fb_helper_connector = fb_helper->connector_info[i];
	drm_connector_unreference(fb_helper_connector->connector);

	for (j = i + 1; j < fb_helper->connector_count; j++) {
		fb_helper->connector_info[j - 1] = fb_helper->connector_info[j];
	}
	fb_helper->connector_count--;
	kfree(fb_helper_connector);

	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_remove_one_connector);

static void drm_fb_helper_save_lut_atomic(struct drm_crtc *crtc, struct drm_fb_helper *helper)
{
	uint16_t *r_base, *g_base, *b_base;
	int i;

	if (helper->funcs->gamma_get == NULL)
		return;

	r_base = crtc->gamma_store;
	g_base = r_base + crtc->gamma_size;
	b_base = g_base + crtc->gamma_size;

	for (i = 0; i < crtc->gamma_size; i++)
		helper->funcs->gamma_get(crtc, &r_base[i], &g_base[i], &b_base[i], i);
}

static void drm_fb_helper_restore_lut_atomic(struct drm_crtc *crtc)
{
	uint16_t *r_base, *g_base, *b_base;

	if (crtc->funcs->gamma_set == NULL)
		return;

	r_base = crtc->gamma_store;
	g_base = r_base + crtc->gamma_size;
	b_base = g_base + crtc->gamma_size;

	crtc->funcs->gamma_set(crtc, r_base, g_base, b_base, crtc->gamma_size);
}

/**
 * drm_fb_helper_debug_enter - implementation for ->fb_debug_enter
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_debug_enter(struct fb_info *info)
{
	struct drm_fb_helper *helper = info->par;
	const struct drm_crtc_helper_funcs *funcs;
	int i;

	list_for_each_entry(helper, &kernel_fb_helper_list, kernel_fb_list) {
		for (i = 0; i < helper->crtc_count; i++) {
			struct drm_mode_set *mode_set =
				&helper->crtc_info[i].mode_set;

			if (!mode_set->crtc->enabled)
				continue;

			funcs =	mode_set->crtc->helper_private;
			drm_fb_helper_save_lut_atomic(mode_set->crtc, helper);
			funcs->mode_set_base_atomic(mode_set->crtc,
						    mode_set->fb,
						    mode_set->x,
						    mode_set->y,
						    ENTER_ATOMIC_MODE_SET);
		}
	}

	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_debug_enter);

/* Find the real fb for a given fb helper CRTC */
static struct drm_framebuffer *drm_mode_config_fb(struct drm_crtc *crtc)
{
	struct drm_device *dev = crtc->dev;
	struct drm_crtc *c;

	drm_for_each_crtc(c, dev) {
		if (crtc->base.id == c->base.id)
			return c->primary->fb;
	}

	return NULL;
}

/**
 * drm_fb_helper_debug_leave - implementation for ->fb_debug_leave
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_debug_leave(struct fb_info *info)
{
	struct drm_fb_helper *helper = info->par;
	struct drm_crtc *crtc;
	const struct drm_crtc_helper_funcs *funcs;
	struct drm_framebuffer *fb;
	int i;

	for (i = 0; i < helper->crtc_count; i++) {
		struct drm_mode_set *mode_set = &helper->crtc_info[i].mode_set;
		crtc = mode_set->crtc;
		funcs = crtc->helper_private;
		fb = drm_mode_config_fb(crtc);

		if (!crtc->enabled)
			continue;

		if (!fb) {
			DRM_ERROR("no fb to restore??\n");
			continue;
		}

		drm_fb_helper_restore_lut_atomic(mode_set->crtc);
		funcs->mode_set_base_atomic(mode_set->crtc, fb, crtc->x,
					    crtc->y, LEAVE_ATOMIC_MODE_SET);
	}

	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_debug_leave);

static int restore_fbdev_mode_atomic(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	struct drm_plane *plane;
	struct drm_atomic_state *state;
	int i, ret;
	unsigned plane_mask;

	state = drm_atomic_state_alloc(dev);
	if (!state)
		return -ENOMEM;

	state->acquire_ctx = dev->mode_config.acquire_ctx;
retry:
	plane_mask = 0;
	drm_for_each_plane(plane, dev) {
		struct drm_plane_state *plane_state;

		plane_state = drm_atomic_get_plane_state(state, plane);
		if (IS_ERR(plane_state)) {
			ret = PTR_ERR(plane_state);
			goto fail;
		}

		plane_state->rotation = DRM_ROTATE_0;

		plane->old_fb = plane->fb;
		plane_mask |= 1 << drm_plane_index(plane);

		/* disable non-primary: */
		if (plane->type == DRM_PLANE_TYPE_PRIMARY)
			continue;

		ret = __drm_atomic_helper_disable_plane(plane, plane_state);
		if (ret != 0)
			goto fail;
	}

	for(i = 0; i < fb_helper->crtc_count; i++) {
		struct drm_mode_set *mode_set = &fb_helper->crtc_info[i].mode_set;

		ret = __drm_atomic_helper_set_config(mode_set, state);
		if (ret != 0)
			goto fail;
	}

	ret = drm_atomic_commit(state);

fail:
	drm_atomic_clean_old_fb(dev, plane_mask, ret);

	if (ret == -EDEADLK)
		goto backoff;

	if (ret != 0)
		drm_atomic_state_free(state);

	return ret;

backoff:
	drm_atomic_state_clear(state);
	drm_atomic_legacy_backoff(state);

	goto retry;
}

static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	struct drm_plane *plane;
	int i;

	drm_warn_on_modeset_not_all_locked(dev);

	if (dev->mode_config.funcs->atomic_commit)
		return restore_fbdev_mode_atomic(fb_helper);

	drm_for_each_plane(plane, dev) {
		if (plane->type != DRM_PLANE_TYPE_PRIMARY)
			drm_plane_force_disable(plane);

		if (dev->mode_config.rotation_property) {
			drm_mode_plane_set_obj_prop(plane,
						    dev->mode_config.rotation_property,
						    DRM_ROTATE_0);
		}
	}

	for (i = 0; i < fb_helper->crtc_count; i++) {
		struct drm_mode_set *mode_set = &fb_helper->crtc_info[i].mode_set;
		struct drm_crtc *crtc = mode_set->crtc;
		int ret;

		if (crtc->funcs->cursor_set2) {
			ret = crtc->funcs->cursor_set2(crtc, NULL, 0, 0, 0, 0, 0);
			if (ret)
				return ret;
		} else if (crtc->funcs->cursor_set) {
			ret = crtc->funcs->cursor_set(crtc, NULL, 0, 0, 0);
			if (ret)
				return ret;
		}

		ret = drm_mode_set_config_internal(mode_set);
		if (ret)
			return ret;
	}

	return 0;
}

/**
 * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration
 * @fb_helper: fbcon to restore
 *
 * This should be called from driver's drm ->lastclose callback
 * when implementing an fbcon on top of kms using this helper. This ensures that
 * the user isn't greeted with a black screen when e.g. X dies.
 *
 * RETURNS:
 * Zero if everything went ok, negative error code otherwise.
 */
int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	bool do_delayed;
	int ret;

	if (!drm_fbdev_emulation)
		return -ENODEV;

	drm_modeset_lock_all(dev);
	ret = restore_fbdev_mode(fb_helper);

	do_delayed = fb_helper->delayed_hotplug;
	if (do_delayed)
		fb_helper->delayed_hotplug = false;
	drm_modeset_unlock_all(dev);

	if (do_delayed)
		drm_fb_helper_hotplug_event(fb_helper);
	return ret;
}
EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked);

static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	struct drm_crtc *crtc;
	int bound = 0, crtcs_bound = 0;

	/* Sometimes user space wants everything disabled, so don't steal the
	 * display if there's a master. */
	if (READ_ONCE(dev->master))
		return false;

	drm_for_each_crtc(crtc, dev) {
		if (crtc->primary->fb)
			crtcs_bound++;
		if (crtc->primary->fb == fb_helper->fb)
			bound++;
	}

	if (bound < crtcs_bound)
		return false;

	return true;
}

#ifdef CONFIG_MAGIC_SYSRQ
/*
 * restore fbcon display for all kms driver's using this helper, used for sysrq
 * and panic handling.
 */
static bool drm_fb_helper_force_kernel_mode(void)
{
	bool ret, error = false;
	struct drm_fb_helper *helper;

	if (list_empty(&kernel_fb_helper_list))
		return false;

	list_for_each_entry(helper, &kernel_fb_helper_list, kernel_fb_list) {
		struct drm_device *dev = helper->dev;

		if (dev->switch_power_state == DRM_SWITCH_POWER_OFF)
			continue;

		drm_modeset_lock_all(dev);
		ret = restore_fbdev_mode(helper);
		if (ret)
			error = true;
		drm_modeset_unlock_all(dev);
	}
	return error;
}

static void drm_fb_helper_restore_work_fn(struct work_struct *ignored)
{
	bool ret;
	ret = drm_fb_helper_force_kernel_mode();
	if (ret == true)
		DRM_ERROR("Failed to restore crtc configuration\n");
}
static DECLARE_WORK(drm_fb_helper_restore_work, drm_fb_helper_restore_work_fn);

static void drm_fb_helper_sysrq(int dummy1)
{
	schedule_work(&drm_fb_helper_restore_work);
}

static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = {
	.handler = drm_fb_helper_sysrq,
	.help_msg = "force-fb(V)",
	.action_msg = "Restore framebuffer console",
};
#else
static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { };
#endif

static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_device *dev = fb_helper->dev;
	struct drm_crtc *crtc;
	struct drm_connector *connector;
	int i, j;

	/*
	 * For each CRTC in this fb, turn the connectors on/off.
	 */
	drm_modeset_lock_all(dev);
	if (!drm_fb_helper_is_bound(fb_helper)) {
		drm_modeset_unlock_all(dev);
		return;
	}

	for (i = 0; i < fb_helper->crtc_count; i++) {
		crtc = fb_helper->crtc_info[i].mode_set.crtc;

		if (!crtc->enabled)
			continue;

		/* Walk the connectors & encoders on this fb turning them on/off */
		for (j = 0; j < fb_helper->connector_count; j++) {
			connector = fb_helper->connector_info[j]->connector;
			connector->funcs->dpms(connector, dpms_mode);
			drm_object_property_set_value(&connector->base,
				dev->mode_config.dpms_property, dpms_mode);
		}
	}
	drm_modeset_unlock_all(dev);
}

/**
 * drm_fb_helper_blank - implementation for ->fb_blank
 * @blank: desired blanking state
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_blank(int blank, struct fb_info *info)
{
	if (oops_in_progress)
		return -EBUSY;

	switch (blank) {
	/* Display: On; HSync: On, VSync: On */
	case FB_BLANK_UNBLANK:
		drm_fb_helper_dpms(info, DRM_MODE_DPMS_ON);
		break;
	/* Display: Off; HSync: On, VSync: On */
	case FB_BLANK_NORMAL:
		drm_fb_helper_dpms(info, DRM_MODE_DPMS_STANDBY);
		break;
	/* Display: Off; HSync: Off, VSync: On */
	case FB_BLANK_HSYNC_SUSPEND:
		drm_fb_helper_dpms(info, DRM_MODE_DPMS_STANDBY);
		break;
	/* Display: Off; HSync: On, VSync: Off */
	case FB_BLANK_VSYNC_SUSPEND:
		drm_fb_helper_dpms(info, DRM_MODE_DPMS_SUSPEND);
		break;
	/* Display: Off; HSync: Off, VSync: Off */
	case FB_BLANK_POWERDOWN:
		drm_fb_helper_dpms(info, DRM_MODE_DPMS_OFF);
		break;
	}
	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_blank);

static void drm_fb_helper_modeset_release(struct drm_fb_helper *helper,
					  struct drm_mode_set *modeset)
{
	int i;

	for (i = 0; i < modeset->num_connectors; i++) {
		drm_connector_unreference(modeset->connectors[i]);
		modeset->connectors[i] = NULL;
	}
	modeset->num_connectors = 0;

	drm_mode_destroy(helper->dev, modeset->mode);
	modeset->mode = NULL;

	/* FIXME should hold a ref? */
	modeset->fb = NULL;
}

static void drm_fb_helper_crtc_free(struct drm_fb_helper *helper)
{
	int i;

	for (i = 0; i < helper->connector_count; i++) {
		drm_connector_unreference(helper->connector_info[i]->connector);
		kfree(helper->connector_info[i]);
	}
	kfree(helper->connector_info);

	for (i = 0; i < helper->crtc_count; i++) {
		struct drm_mode_set *modeset = &helper->crtc_info[i].mode_set;

		drm_fb_helper_modeset_release(helper, modeset);
		kfree(modeset->connectors);
	}
	kfree(helper->crtc_info);
}

static void drm_fb_helper_resume_worker(struct work_struct *work)
{
	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
						    resume_work);

	console_lock();
	fb_set_suspend(helper->fbdev, 0);
	console_unlock();
}

static void drm_fb_helper_dirty_work(struct work_struct *work)
{
	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
						    dirty_work);
	struct drm_clip_rect *clip = &helper->dirty_clip;
	struct drm_clip_rect clip_copy;
	unsigned long flags;

	spin_lock_irqsave(&helper->dirty_lock, flags);
	clip_copy = *clip;
	clip->x1 = clip->y1 = ~0;
	clip->x2 = clip->y2 = 0;
	spin_unlock_irqrestore(&helper->dirty_lock, flags);

	/* call dirty callback only when it has been really touched */
	if (clip_copy.x1 < clip_copy.x2 && clip_copy.y1 < clip_copy.y2)
		helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
}

/**
 * drm_fb_helper_prepare - setup a drm_fb_helper structure
 * @dev: DRM device
 * @helper: driver-allocated fbdev helper structure to set up
 * @funcs: pointer to structure of functions associate with this helper
 *
 * Sets up the bare minimum to make the framebuffer helper usable. This is
 * useful to implement race-free initialization of the polling helpers.
 */
void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
			   const struct drm_fb_helper_funcs *funcs)
{
	INIT_LIST_HEAD(&helper->kernel_fb_list);
	spin_lock_init(&helper->dirty_lock);
	INIT_WORK(&helper->resume_work, drm_fb_helper_resume_worker);
	INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
	helper->dirty_clip.x1 = helper->dirty_clip.y1 = ~0;
	helper->funcs = funcs;
	helper->dev = dev;
}
EXPORT_SYMBOL(drm_fb_helper_prepare);

/**
 * drm_fb_helper_init - initialize a drm_fb_helper structure
 * @dev: drm device
 * @fb_helper: driver-allocated fbdev helper structure to initialize
 * @crtc_count: maximum number of crtcs to support in this fbdev emulation
 * @max_conn_count: max connector count
 *
 * This allocates the structures for the fbdev helper with the given limits.
 * Note that this won't yet touch the hardware (through the driver interfaces)
 * nor register the fbdev. This is only done in drm_fb_helper_initial_config()
 * to allow driver writes more control over the exact init sequence.
 *
 * Drivers must call drm_fb_helper_prepare() before calling this function.
 *
 * RETURNS:
 * Zero if everything went ok, nonzero otherwise.
 */
int drm_fb_helper_init(struct drm_device *dev,
		       struct drm_fb_helper *fb_helper,
		       int crtc_count, int max_conn_count)
{
	struct drm_crtc *crtc;
	int i;

	if (!drm_fbdev_emulation)
		return 0;

	if (!max_conn_count)
		return -EINVAL;

	fb_helper->crtc_info = kcalloc(crtc_count, sizeof(struct drm_fb_helper_crtc), GFP_KERNEL);
	if (!fb_helper->crtc_info)
		return -ENOMEM;

	fb_helper->crtc_count = crtc_count;
	fb_helper->connector_info = kcalloc(dev->mode_config.num_connector, sizeof(struct drm_fb_helper_connector *), GFP_KERNEL);
	if (!fb_helper->connector_info) {
		kfree(fb_helper->crtc_info);
		return -ENOMEM;
	}
	fb_helper->connector_info_alloc_count = dev->mode_config.num_connector;
	fb_helper->connector_count = 0;

	for (i = 0; i < crtc_count; i++) {
		fb_helper->crtc_info[i].mode_set.connectors =
			kcalloc(max_conn_count,
				sizeof(struct drm_connector *),
				GFP_KERNEL);

		if (!fb_helper->crtc_info[i].mode_set.connectors)
			goto out_free;
		fb_helper->crtc_info[i].mode_set.num_connectors = 0;
	}

	i = 0;
	drm_for_each_crtc(crtc, dev) {
		fb_helper->crtc_info[i].mode_set.crtc = crtc;
		i++;
	}

	return 0;
out_free:
	drm_fb_helper_crtc_free(fb_helper);
	return -ENOMEM;
}
EXPORT_SYMBOL(drm_fb_helper_init);

/**
 * drm_fb_helper_alloc_fbi - allocate fb_info and some of its members
 * @fb_helper: driver-allocated fbdev helper
 *
 * A helper to alloc fb_info and the members cmap and apertures. Called
 * by the driver within the fb_probe fb_helper callback function.
 *
 * RETURNS:
 * fb_info pointer if things went okay, pointer containing error code
 * otherwise
 */
struct fb_info *drm_fb_helper_alloc_fbi(struct drm_fb_helper *fb_helper)
{
	struct device *dev = fb_helper->dev->dev;
	struct fb_info *info;
	int ret;

	info = framebuffer_alloc(0, dev);
	if (!info)
		return ERR_PTR(-ENOMEM);

	ret = fb_alloc_cmap(&info->cmap, 256, 0);
	if (ret)
		goto err_release;

	info->apertures = alloc_apertures(1);
	if (!info->apertures) {
		ret = -ENOMEM;
		goto err_free_cmap;
	}

	fb_helper->fbdev = info;

	return info;

err_free_cmap:
	fb_dealloc_cmap(&info->cmap);
err_release:
	framebuffer_release(info);
	return ERR_PTR(ret);
}
EXPORT_SYMBOL(drm_fb_helper_alloc_fbi);

/**
 * drm_fb_helper_unregister_fbi - unregister fb_info framebuffer device
 * @fb_helper: driver-allocated fbdev helper
 *
 * A wrapper around unregister_framebuffer, to release the fb_info
 * framebuffer device
 */
void drm_fb_helper_unregister_fbi(struct drm_fb_helper *fb_helper)
{
	if (fb_helper && fb_helper->fbdev)
		unregister_framebuffer(fb_helper->fbdev);
}
EXPORT_SYMBOL(drm_fb_helper_unregister_fbi);

/**
 * drm_fb_helper_release_fbi - dealloc fb_info and its members
 * @fb_helper: driver-allocated fbdev helper
 *
 * A helper to free memory taken by fb_info and the members cmap and
 * apertures
 */
void drm_fb_helper_release_fbi(struct drm_fb_helper *fb_helper)
{
	if (fb_helper) {
		struct fb_info *info = fb_helper->fbdev;

		if (info) {
			if (info->cmap.len)
				fb_dealloc_cmap(&info->cmap);
			framebuffer_release(info);
		}

		fb_helper->fbdev = NULL;
	}
}
EXPORT_SYMBOL(drm_fb_helper_release_fbi);

void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
{
	if (!drm_fbdev_emulation)
		return;

	if (!list_empty(&fb_helper->kernel_fb_list)) {
		list_del(&fb_helper->kernel_fb_list);
		if (list_empty(&kernel_fb_helper_list)) {
			unregister_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
		}
	}

	drm_fb_helper_crtc_free(fb_helper);

}
EXPORT_SYMBOL(drm_fb_helper_fini);

/**
 * drm_fb_helper_unlink_fbi - wrapper around unlink_framebuffer
 * @fb_helper: driver-allocated fbdev helper
 *
 * A wrapper around unlink_framebuffer implemented by fbdev core
 */
void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper)
{
	if (fb_helper && fb_helper->fbdev)
		unlink_framebuffer(fb_helper->fbdev);
}
EXPORT_SYMBOL(drm_fb_helper_unlink_fbi);

static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y,
				u32 width, u32 height)
{
	struct drm_fb_helper *helper = info->par;
	struct drm_clip_rect *clip = &helper->dirty_clip;
	unsigned long flags;

	if (!helper->fb->funcs->dirty)
		return;

	spin_lock_irqsave(&helper->dirty_lock, flags);
	clip->x1 = min_t(u32, clip->x1, x);
	clip->y1 = min_t(u32, clip->y1, y);
	clip->x2 = max_t(u32, clip->x2, x + width);
	clip->y2 = max_t(u32, clip->y2, y + height);
	spin_unlock_irqrestore(&helper->dirty_lock, flags);

	schedule_work(&helper->dirty_work);
}

/**
 * drm_fb_helper_deferred_io() - fbdev deferred_io callback function
 * @info: fb_info struct pointer
 * @pagelist: list of dirty mmap framebuffer pages
 *
 * This function is used as the &fb_deferred_io ->deferred_io
 * callback function for flushing the fbdev mmap writes.
 */
void drm_fb_helper_deferred_io(struct fb_info *info,
			       struct list_head *pagelist)
{
	unsigned long start, end, min, max;
	struct page *page;
	u32 y1, y2;

	min = ULONG_MAX;
	max = 0;
	list_for_each_entry(page, pagelist, lru) {
		start = page->index << PAGE_SHIFT;
		end = start + PAGE_SIZE - 1;
		min = min(min, start);
		max = max(max, end);
	}

	if (min < max) {
		y1 = min / info->fix.line_length;
		y2 = min_t(u32, DIV_ROUND_UP(max, info->fix.line_length),
			   info->var.yres);
		drm_fb_helper_dirty(info, 0, y1, info->var.xres, y2 - y1);
	}
}
EXPORT_SYMBOL(drm_fb_helper_deferred_io);

/**
 * drm_fb_helper_sys_read - wrapper around fb_sys_read
 * @info: fb_info struct pointer
 * @buf: userspace buffer to read from framebuffer memory
 * @count: number of bytes to read from framebuffer memory
 * @ppos: read offset within framebuffer memory
 *
 * A wrapper around fb_sys_read implemented by fbdev core
 */
ssize_t drm_fb_helper_sys_read(struct fb_info *info, char __user *buf,
			       size_t count, loff_t *ppos)
{
	return fb_sys_read(info, buf, count, ppos);
}
EXPORT_SYMBOL(drm_fb_helper_sys_read);

/**
 * drm_fb_helper_sys_write - wrapper around fb_sys_write
 * @info: fb_info struct pointer
 * @buf: userspace buffer to write to framebuffer memory
 * @count: number of bytes to write to framebuffer memory
 * @ppos: write offset within framebuffer memory
 *
 * A wrapper around fb_sys_write implemented by fbdev core
 */
ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
				size_t count, loff_t *ppos)
{
	ssize_t ret;

	ret = fb_sys_write(info, buf, count, ppos);
	if (ret > 0)
		drm_fb_helper_dirty(info, 0, 0, info->var.xres,
				    info->var.yres);

	return ret;
}
EXPORT_SYMBOL(drm_fb_helper_sys_write);

/**
 * drm_fb_helper_sys_fillrect - wrapper around sys_fillrect
 * @info: fbdev registered by the helper
 * @rect: info about rectangle to fill
 *
 * A wrapper around sys_fillrect implemented by fbdev core
 */
void drm_fb_helper_sys_fillrect(struct fb_info *info,
				const struct fb_fillrect *rect)
{
	sys_fillrect(info, rect);
	drm_fb_helper_dirty(info, rect->dx, rect->dy,
			    rect->width, rect->height);
}
EXPORT_SYMBOL(drm_fb_helper_sys_fillrect);

/**
 * drm_fb_helper_sys_copyarea - wrapper around sys_copyarea
 * @info: fbdev registered by the helper
 * @area: info about area to copy
 *
 * A wrapper around sys_copyarea implemented by fbdev core
 */
void drm_fb_helper_sys_copyarea(struct fb_info *info,
				const struct fb_copyarea *area)
{
	sys_copyarea(info, area);
	drm_fb_helper_dirty(info, area->dx, area->dy,
			    area->width, area->height);
}
EXPORT_SYMBOL(drm_fb_helper_sys_copyarea);

/**
 * drm_fb_helper_sys_imageblit - wrapper around sys_imageblit
 * @info: fbdev registered by the helper
 * @image: info about image to blit
 *
 * A wrapper around sys_imageblit implemented by fbdev core
 */
void drm_fb_helper_sys_imageblit(struct fb_info *info,
				 const struct fb_image *image)
{
	sys_imageblit(info, image);
	drm_fb_helper_dirty(info, image->dx, image->dy,
			    image->width, image->height);
}
EXPORT_SYMBOL(drm_fb_helper_sys_imageblit);

/**
 * drm_fb_helper_cfb_fillrect - wrapper around cfb_fillrect
 * @info: fbdev registered by the helper
 * @rect: info about rectangle to fill
 *
 * A wrapper around cfb_imageblit implemented by fbdev core
 */
void drm_fb_helper_cfb_fillrect(struct fb_info *info,
				const struct fb_fillrect *rect)
{
	cfb_fillrect(info, rect);
	drm_fb_helper_dirty(info, rect->dx, rect->dy,
			    rect->width, rect->height);
}
EXPORT_SYMBOL(drm_fb_helper_cfb_fillrect);

/**
 * drm_fb_helper_cfb_copyarea - wrapper around cfb_copyarea
 * @info: fbdev registered by the helper
 * @area: info about area to copy
 *
 * A wrapper around cfb_copyarea implemented by fbdev core
 */
void drm_fb_helper_cfb_copyarea(struct fb_info *info,
				const struct fb_copyarea *area)
{
	cfb_copyarea(info, area);
	drm_fb_helper_dirty(info, area->dx, area->dy,
			    area->width, area->height);
}
EXPORT_SYMBOL(drm_fb_helper_cfb_copyarea);

/**
 * drm_fb_helper_cfb_imageblit - wrapper around cfb_imageblit
 * @info: fbdev registered by the helper
 * @image: info about image to blit
 *
 * A wrapper around cfb_imageblit implemented by fbdev core
 */
void drm_fb_helper_cfb_imageblit(struct fb_info *info,
				 const struct fb_image *image)
{
	cfb_imageblit(info, image);
	drm_fb_helper_dirty(info, image->dx, image->dy,
			    image->width, image->height);
}
EXPORT_SYMBOL(drm_fb_helper_cfb_imageblit);

/**
 * drm_fb_helper_set_suspend - wrapper around fb_set_suspend
 * @fb_helper: driver-allocated fbdev helper
 * @suspend: whether to suspend or resume
 *
 * A wrapper around fb_set_suspend implemented by fbdev core.
 * Use drm_fb_helper_set_suspend_unlocked() if you don't need to take
 * the lock yourself
 */
void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, bool suspend)
{
	if (fb_helper && fb_helper->fbdev)
		fb_set_suspend(fb_helper->fbdev, suspend);
}
EXPORT_SYMBOL(drm_fb_helper_set_suspend);

/**
 * drm_fb_helper_set_suspend_unlocked - wrapper around fb_set_suspend that also
 *                                      takes the console lock
 * @fb_helper: driver-allocated fbdev helper
 * @suspend: whether to suspend or resume
 *
 * A wrapper around fb_set_suspend() that takes the console lock. If the lock
 * isn't available on resume, a worker is tasked with waiting for the lock
 * to become available. The console lock can be pretty contented on resume
 * due to all the printk activity.
 *
 * This function can be called multiple times with the same state since
 * &fb_info->state is checked to see if fbdev is running or not before locking.
 *
 * Use drm_fb_helper_set_suspend() if you need to take the lock yourself.
 */
void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
					bool suspend)
{
	if (!fb_helper || !fb_helper->fbdev)
		return;

	/* make sure there's no pending/ongoing resume */
	flush_work(&fb_helper->resume_work);

	if (suspend) {
		if (fb_helper->fbdev->state != FBINFO_STATE_RUNNING)
			return;

		console_lock();

	} else {
		if (fb_helper->fbdev->state == FBINFO_STATE_RUNNING)
			return;

		if (!console_trylock()) {
			schedule_work(&fb_helper->resume_work);
			return;
		}
	}

	fb_set_suspend(fb_helper->fbdev, suspend);
	console_unlock();
}
EXPORT_SYMBOL(drm_fb_helper_set_suspend_unlocked);

static int setcolreg(struct drm_crtc *crtc, u16 red, u16 green,
		     u16 blue, u16 regno, struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_framebuffer *fb = fb_helper->fb;

	if (info->fix.visual == FB_VISUAL_TRUECOLOR) {
		u32 *palette;
		u32 value;
		/* place color in psuedopalette */
		if (regno > 16)
			return -EINVAL;
		palette = (u32 *)info->pseudo_palette;
		red >>= (16 - info->var.red.length);
		green >>= (16 - info->var.green.length);
		blue >>= (16 - info->var.blue.length);
		value = (red << info->var.red.offset) |
			(green << info->var.green.offset) |
			(blue << info->var.blue.offset);
		if (info->var.transp.length > 0) {
			u32 mask = (1 << info->var.transp.length) - 1;
			mask <<= info->var.transp.offset;
			value |= mask;
		}
		palette[regno] = value;
		return 0;
	}

	/*
	 * The driver really shouldn't advertise pseudo/directcolor
	 * visuals if it can't deal with the palette.
	 */
	if (WARN_ON(!fb_helper->funcs->gamma_set ||
		    !fb_helper->funcs->gamma_get))
		return -EINVAL;

	WARN_ON(fb->bits_per_pixel != 8);

	fb_helper->funcs->gamma_set(crtc, red, green, blue, regno);

	return 0;
}

/**
 * drm_fb_helper_setcmap - implementation for ->fb_setcmap
 * @cmap: cmap to set
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_device *dev = fb_helper->dev;
	const struct drm_crtc_helper_funcs *crtc_funcs;
	u16 *red, *green, *blue, *transp;
	struct drm_crtc *crtc;
	int i, j, rc = 0;
	int start;

	if (oops_in_progress)
		return -EBUSY;

	drm_modeset_lock_all(dev);
	if (!drm_fb_helper_is_bound(fb_helper)) {
		drm_modeset_unlock_all(dev);
		return -EBUSY;
	}

	for (i = 0; i < fb_helper->crtc_count; i++) {
		crtc = fb_helper->crtc_info[i].mode_set.crtc;
		crtc_funcs = crtc->helper_private;

		red = cmap->red;
		green = cmap->green;
		blue = cmap->blue;
		transp = cmap->transp;
		start = cmap->start;

		for (j = 0; j < cmap->len; j++) {
			u16 hred, hgreen, hblue, htransp = 0xffff;

			hred = *red++;
			hgreen = *green++;
			hblue = *blue++;

			if (transp)
				htransp = *transp++;

			rc = setcolreg(crtc, hred, hgreen, hblue, start++, info);
			if (rc)
				goto out;
		}
		if (crtc_funcs->load_lut)
			crtc_funcs->load_lut(crtc);
	}
 out:
	drm_modeset_unlock_all(dev);
	return rc;
}
EXPORT_SYMBOL(drm_fb_helper_setcmap);

/**
 * drm_fb_helper_check_var - implementation for ->fb_check_var
 * @var: screeninfo to check
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
			    struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_framebuffer *fb = fb_helper->fb;
	int depth;

	if (var->pixclock != 0 || in_dbg_master())
		return -EINVAL;

	/* Need to resize the fb object !!! */
	if (var->bits_per_pixel > fb->bits_per_pixel ||
	    var->xres > fb->width || var->yres > fb->height ||
	    var->xres_virtual > fb->width || var->yres_virtual > fb->height) {
		DRM_DEBUG("fb userspace requested width/height/bpp is greater than current fb "
			  "request %dx%d-%d (virtual %dx%d) > %dx%d-%d\n",
			  var->xres, var->yres, var->bits_per_pixel,
			  var->xres_virtual, var->yres_virtual,
			  fb->width, fb->height, fb->bits_per_pixel);
		return -EINVAL;
	}

	switch (var->bits_per_pixel) {
	case 16:
		depth = (var->green.length == 6) ? 16 : 15;
		break;
	case 32:
		depth = (var->transp.length > 0) ? 32 : 24;
		break;
	default:
		depth = var->bits_per_pixel;
		break;
	}

	switch (depth) {
	case 8:
		var->red.offset = 0;
		var->green.offset = 0;
		var->blue.offset = 0;
		var->red.length = 8;
		var->green.length = 8;
		var->blue.length = 8;
		var->transp.length = 0;
		var->transp.offset = 0;
		break;
	case 15:
		var->red.offset = 10;
		var->green.offset = 5;
		var->blue.offset = 0;
		var->red.length = 5;
		var->green.length = 5;
		var->blue.length = 5;
		var->transp.length = 1;
		var->transp.offset = 15;
		break;
	case 16:
		var->red.offset = 11;
		var->green.offset = 5;
		var->blue.offset = 0;
		var->red.length = 5;
		var->green.length = 6;
		var->blue.length = 5;
		var->transp.length = 0;
		var->transp.offset = 0;
		break;
	case 24:
		var->red.offset = 16;
		var->green.offset = 8;
		var->blue.offset = 0;
		var->red.length = 8;
		var->green.length = 8;
		var->blue.length = 8;
		var->transp.length = 0;
		var->transp.offset = 0;
		break;
	case 32:
		var->red.offset = 16;
		var->green.offset = 8;
		var->blue.offset = 0;
		var->red.length = 8;
		var->green.length = 8;
		var->blue.length = 8;
		var->transp.length = 8;
		var->transp.offset = 24;
		break;
	default:
		return -EINVAL;
	}
	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_check_var);

/**
 * drm_fb_helper_set_par - implementation for ->fb_set_par
 * @info: fbdev registered by the helper
 *
 * This will let fbcon do the mode init and is called at initialization time by
 * the fbdev core when registering the driver, and later on through the hotplug
 * callback.
 */
int drm_fb_helper_set_par(struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct fb_var_screeninfo *var = &info->var;

	if (oops_in_progress)
		return -EBUSY;

	if (var->pixclock != 0) {
		DRM_ERROR("PIXEL CLOCK SET\n");
		return -EINVAL;
	}

	drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper);

	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_set_par);

static int pan_display_atomic(struct fb_var_screeninfo *var,
			      struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_device *dev = fb_helper->dev;
	struct drm_atomic_state *state;
	struct drm_plane *plane;
	int i, ret;
	unsigned plane_mask;

	state = drm_atomic_state_alloc(dev);
	if (!state)
		return -ENOMEM;

	state->acquire_ctx = dev->mode_config.acquire_ctx;
retry:
	plane_mask = 0;
	for(i = 0; i < fb_helper->crtc_count; i++) {
		struct drm_mode_set *mode_set;

		mode_set = &fb_helper->crtc_info[i].mode_set;

		mode_set->x = var->xoffset;
		mode_set->y = var->yoffset;

		ret = __drm_atomic_helper_set_config(mode_set, state);
		if (ret != 0)
			goto fail;

		plane = mode_set->crtc->primary;
		plane_mask |= (1 << drm_plane_index(plane));
		plane->old_fb = plane->fb;
	}

	ret = drm_atomic_commit(state);
	if (ret != 0)
		goto fail;

	info->var.xoffset = var->xoffset;
	info->var.yoffset = var->yoffset;


fail:
	drm_atomic_clean_old_fb(dev, plane_mask, ret);

	if (ret == -EDEADLK)
		goto backoff;

	if (ret != 0)
		drm_atomic_state_free(state);

	return ret;

backoff:
	drm_atomic_state_clear(state);
	drm_atomic_legacy_backoff(state);

	goto retry;
}

/**
 * drm_fb_helper_pan_display - implementation for ->fb_pan_display
 * @var: updated screen information
 * @info: fbdev registered by the helper
 */
int drm_fb_helper_pan_display(struct fb_var_screeninfo *var,
			      struct fb_info *info)
{
	struct drm_fb_helper *fb_helper = info->par;
	struct drm_device *dev = fb_helper->dev;
	struct drm_mode_set *modeset;
	int ret = 0;
	int i;

	if (oops_in_progress)
		return -EBUSY;

	drm_modeset_lock_all(dev);
	if (!drm_fb_helper_is_bound(fb_helper)) {
		drm_modeset_unlock_all(dev);
		return -EBUSY;
	}

	if (dev->mode_config.funcs->atomic_commit) {
		ret = pan_display_atomic(var, info);
		goto unlock;
	}

	for (i = 0; i < fb_helper->crtc_count; i++) {
		modeset = &fb_helper->crtc_info[i].mode_set;

		modeset->x = var->xoffset;
		modeset->y = var->yoffset;

		if (modeset->num_connectors) {
			ret = drm_mode_set_config_internal(modeset);
			if (!ret) {
				info->var.xoffset = var->xoffset;
				info->var.yoffset = var->yoffset;
			}
		}
	}
unlock:
	drm_modeset_unlock_all(dev);
	return ret;
}
EXPORT_SYMBOL(drm_fb_helper_pan_display);

/*
 * Allocates the backing storage and sets up the fbdev info structure through
 * the ->fb_probe callback and then registers the fbdev and sets up the panic
 * notifier.
 */
static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
					 int preferred_bpp)
{
	int ret = 0;
	int crtc_count = 0;
	int i;
	struct fb_info *info;
	struct drm_fb_helper_surface_size sizes;
	int gamma_size = 0;

	memset(&sizes, 0, sizeof(struct drm_fb_helper_surface_size));
	sizes.surface_depth = 24;
	sizes.surface_bpp = 32;
	sizes.fb_width = (unsigned)-1;
	sizes.fb_height = (unsigned)-1;

	/* if driver picks 8 or 16 by default use that
	   for both depth/bpp */
	if (preferred_bpp != sizes.surface_bpp)
		sizes.surface_depth = sizes.surface_bpp = preferred_bpp;

	/* first up get a count of crtcs now in use and new min/maxes width/heights */
	for (i = 0; i < fb_helper->connector_count; i++) {
		struct drm_fb_helper_connector *fb_helper_conn = fb_helper->connector_info[i];
		struct drm_cmdline_mode *cmdline_mode;

		cmdline_mode = &fb_helper_conn->connector->cmdline_mode;

		if (cmdline_mode->bpp_specified) {
			switch (cmdline_mode->bpp) {
			case 8:
				sizes.surface_depth = sizes.surface_bpp = 8;
				break;
			case 15:
				sizes.surface_depth = 15;
				sizes.surface_bpp = 16;
				break;
			case 16:
				sizes.surface_depth = sizes.surface_bpp = 16;
				break;
			case 24:
				sizes.surface_depth = sizes.surface_bpp = 24;
				break;
			case 32:
				sizes.surface_depth = 24;
				sizes.surface_bpp = 32;
				break;
			}
			break;
		}
	}

	crtc_count = 0;
	for (i = 0; i < fb_helper->crtc_count; i++) {
		struct drm_display_mode *desired_mode;
		struct drm_mode_set *mode_set;
		int x, y, j;
		/* in case of tile group, are we the last tile vert or horiz?
		 * If no tile group you are always the last one both vertically
		 * and horizontally
		 */
		bool lastv = true, lasth = true;

		desired_mode = fb_helper->crtc_info[i].desired_mode;
		mode_set = &fb_helper->crtc_info[i].mode_set;

		if (!desired_mode)
			continue;

		crtc_count++;

		x = fb_helper->crtc_info[i].x;
		y = fb_helper->crtc_info[i].y;

		if (gamma_size == 0)
			gamma_size = fb_helper->crtc_info[i].mode_set.crtc->gamma_size;

		sizes.surface_width  = max_t(u32, desired_mode->hdisplay + x, sizes.surface_width);
		sizes.surface_height = max_t(u32, desired_mode->vdisplay + y, sizes.surface_height);

		for (j = 0; j < mode_set->num_connectors; j++) {
			struct drm_connector *connector = mode_set->connectors[j];
			if (connector->has_tile) {
				lasth = (connector->tile_h_loc == (connector->num_h_tile - 1));
				lastv = (connector->tile_v_loc == (connector->num_v_tile - 1));
				/* cloning to multiple tiles is just crazy-talk, so: */
				break;
			}
		}

		if (lasth)
			sizes.fb_width  = min_t(u32, desired_mode->hdisplay + x, sizes.fb_width);
		if (lastv)
			sizes.fb_height = min_t(u32, desired_mode->vdisplay + y, sizes.fb_height);
	}

	if (crtc_count == 0 || sizes.fb_width == -1 || sizes.fb_height == -1) {
		/* hmm everyone went away - assume VGA cable just fell out
		   and will come back later. */
		DRM_INFO("Cannot find any crtc or sizes - going 1024x768\n");
		sizes.fb_width = sizes.surface_width = 1024;
		sizes.fb_height = sizes.surface_height = 768;
	}

	/* push down into drivers */
	ret = (*fb_helper->funcs->fb_probe)(fb_helper, &sizes);
	if (ret < 0)
		return ret;

	info = fb_helper->fbdev;

	/*
	 * Set the fb pointer - usually drm_setup_crtcs does this for hotplug
	 * events, but at init time drm_setup_crtcs needs to be called before
	 * the fb is allocated (since we need to figure out the desired size of
	 * the fb before we can allocate it ...). Hence we need to fix things up
	 * here again.
	 */
	for (i = 0; i < fb_helper->crtc_count; i++)
		if (fb_helper->crtc_info[i].mode_set.num_connectors)
			fb_helper->crtc_info[i].mode_set.fb = fb_helper->fb;


	info->var.pixclock = 0;
	if (register_framebuffer(info) < 0)
		return -EINVAL;

	dev_info(fb_helper->dev->dev, "fb%d: %s frame buffer device\n",
			info->node, info->fix.id);

	if (list_empty(&kernel_fb_helper_list)) {
		register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
	}

	list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);

	return 0;
}

/**
 * drm_fb_helper_fill_fix - initializes fixed fbdev information
 * @info: fbdev registered by the helper
 * @pitch: desired pitch
 * @depth: desired depth
 *
 * Helper to fill in the fixed fbdev information useful for a non-accelerated
 * fbdev emulations. Drivers which support acceleration methods which impose
 * additional constraints need to set up their own limits.
 *
 * Drivers should call this (or their equivalent setup code) from their
 * ->fb_probe callback.
 */
void drm_fb_helper_fill_fix(struct fb_info *info, uint32_t pitch,
			    uint32_t depth)
{
	info->fix.type = FB_TYPE_PACKED_PIXELS;
	info->fix.visual = depth == 8 ? FB_VISUAL_PSEUDOCOLOR :
		FB_VISUAL_TRUECOLOR;
	info->fix.mmio_start = 0;
	info->fix.mmio_len = 0;
	info->fix.type_aux = 0;
	info->fix.xpanstep = 1; /* doing it in hw */
	info->fix.ypanstep = 1; /* doing it in hw */
	info->fix.ywrapstep = 0;
	info->fix.accel = FB_ACCEL_NONE;

	info->fix.line_length = pitch;
	return;
}
EXPORT_SYMBOL(drm_fb_helper_fill_fix);

/**
 * drm_fb_helper_fill_var - initalizes variable fbdev information
 * @info: fbdev instance to set up
 * @fb_helper: fb helper instance to use as template
 * @fb_width: desired fb width
 * @fb_height: desired fb height
 *
 * Sets up the variable fbdev metainformation from the given fb helper instance
 * and the drm framebuffer allocated in fb_helper->fb.
 *
 * Drivers should call this (or their equivalent setup code) from their
 * ->fb_probe callback after having allocated the fbdev backing
 * storage framebuffer.
 */
void drm_fb_helper_fill_var(struct fb_info *info, struct drm_fb_helper *fb_helper,
			    uint32_t fb_width, uint32_t fb_height)
{
	struct drm_framebuffer *fb = fb_helper->fb;
	info->pseudo_palette = fb_helper->pseudo_palette;
	info->var.xres_virtual = fb->width;
	info->var.yres_virtual = fb->height;
	info->var.bits_per_pixel = fb->bits_per_pixel;
	info->var.accel_flags = FB_ACCELF_TEXT;
	info->var.xoffset = 0;
	info->var.yoffset = 0;
	info->var.activate = FB_ACTIVATE_NOW;
	info->var.height = -1;
	info->var.width = -1;

	switch (fb->depth) {
	case 8:
		info->var.red.offset = 0;
		info->var.green.offset = 0;
		info->var.blue.offset = 0;
		info->var.red.length = 8; /* 8bit DAC */
		info->var.green.length = 8;
		info->var.blue.length = 8;
		info->var.transp.offset = 0;
		info->var.transp.length = 0;
		break;
	case 15:
		info->var.red.offset = 10;
		info->var.green.offset = 5;
		info->var.blue.offset = 0;
		info->var.red.length = 5;
		info->var.green.length = 5;
		info->var.blue.length = 5;
		info->var.transp.offset = 15;
		info->var.transp.length = 1;
		break;
	case 16:
		info->var.red.offset = 11;
		info->var.green.offset = 5;
		info->var.blue.offset = 0;
		info->var.red.length = 5;
		info->var.green.length = 6;
		info->var.blue.length = 5;
		info->var.transp.offset = 0;
		break;
	case 24:
		info->var.red.offset = 16;
		info->var.green.offset = 8;
		info->var.blue.offset = 0;
		info->var.red.length = 8;
		info->var.green.length = 8;
		info->var.blue.length = 8;
		info->var.transp.offset = 0;
		info->var.transp.length = 0;
		break;
	case 32:
		info->var.red.offset = 16;
		info->var.green.offset = 8;
		info->var.blue.offset = 0;
		info->var.red.length = 8;
		info->var.green.length = 8;
		info->var.blue.length = 8;
		info->var.transp.offset = 24;
		info->var.transp.length = 8;
		break;
	default:
		break;
	}

	info->var.xres = fb_width;
	info->var.yres = fb_height;
}
EXPORT_SYMBOL(drm_fb_helper_fill_var);

static int drm_fb_helper_probe_connector_modes(struct drm_fb_helper *fb_helper,
					       uint32_t maxX,
					       uint32_t maxY)
{
	struct drm_connector *connector;
	int count = 0;
	int i;

	for (i = 0; i < fb_helper->connector_count; i++) {
		connector = fb_helper->connector_info[i]->connector;
		count += connector->funcs->fill_modes(connector, maxX, maxY);
	}

	return count;
}

struct drm_display_mode *drm_has_preferred_mode(struct drm_fb_helper_connector *fb_connector, int width, int height)
{
	struct drm_display_mode *mode;

	list_for_each_entry(mode, &fb_connector->connector->modes, head) {
		if (mode->hdisplay > width ||
		    mode->vdisplay > height)
			continue;
		if (mode->type & DRM_MODE_TYPE_PREFERRED)
			return mode;
	}
	return NULL;
}
EXPORT_SYMBOL(drm_has_preferred_mode);

static bool drm_has_cmdline_mode(struct drm_fb_helper_connector *fb_connector)
{
	return fb_connector->connector->cmdline_mode.specified;
}

struct drm_display_mode *drm_pick_cmdline_mode(struct drm_fb_helper_connector *fb_helper_conn,
						      int width, int height)
{
	struct drm_cmdline_mode *cmdline_mode;
	struct drm_display_mode *mode;
	bool prefer_non_interlace;

	cmdline_mode = &fb_helper_conn->connector->cmdline_mode;
	if (cmdline_mode->specified == false)
		return NULL;

	/* attempt to find a matching mode in the list of modes
	 *  we have gotten so far, if not add a CVT mode that conforms
	 */
	if (cmdline_mode->rb || cmdline_mode->margins)
		goto create_mode;

	prefer_non_interlace = !cmdline_mode->interlace;
again:
	list_for_each_entry(mode, &fb_helper_conn->connector->modes, head) {
		/* check width/height */
		if (mode->hdisplay != cmdline_mode->xres ||
		    mode->vdisplay != cmdline_mode->yres)
			continue;

		if (cmdline_mode->refresh_specified) {
			if (mode->vrefresh != cmdline_mode->refresh)
				continue;
		}

		if (cmdline_mode->interlace) {
			if (!(mode->flags & DRM_MODE_FLAG_INTERLACE))
				continue;
		} else if (prefer_non_interlace) {
			if (mode->flags & DRM_MODE_FLAG_INTERLACE)
				continue;
		}
		return mode;
	}

	if (prefer_non_interlace) {
		prefer_non_interlace = false;
		goto again;
	}

create_mode:
	mode = drm_mode_create_from_cmdline_mode(fb_helper_conn->connector->dev,
						 cmdline_mode);
	list_add(&mode->head, &fb_helper_conn->connector->modes);
	return mode;
}
EXPORT_SYMBOL(drm_pick_cmdline_mode);

static bool drm_connector_enabled(struct drm_connector *connector, bool strict)
{
	bool enable;

	if (strict)
		enable = connector->status == connector_status_connected;
	else
		enable = connector->status != connector_status_disconnected;

	return enable;
}

static void drm_enable_connectors(struct drm_fb_helper *fb_helper,
				  bool *enabled)
{
	bool any_enabled = false;
	struct drm_connector *connector;
	int i = 0;

	for (i = 0; i < fb_helper->connector_count; i++) {
		connector = fb_helper->connector_info[i]->connector;
		enabled[i] = drm_connector_enabled(connector, true);
		DRM_DEBUG_KMS("connector %d enabled? %s\n", connector->base.id,
			  enabled[i] ? "yes" : "no");
		any_enabled |= enabled[i];
	}

	if (any_enabled)
		return;

	for (i = 0; i < fb_helper->connector_count; i++) {
		connector = fb_helper->connector_info[i]->connector;
		enabled[i] = drm_connector_enabled(connector, false);
	}
}

static bool drm_target_cloned(struct drm_fb_helper *fb_helper,
			      struct drm_display_mode **modes,
			      struct drm_fb_offset *offsets,
			      bool *enabled, int width, int height)
{
	int count, i, j;
	bool can_clone = false;
	struct drm_fb_helper_connector *fb_helper_conn;
	struct drm_display_mode *dmt_mode, *mode;

	/* only contemplate cloning in the single crtc case */
	if (fb_helper->crtc_count > 1)
		return false;

	count = 0;
	for (i = 0; i < fb_helper->connector_count; i++) {
		if (enabled[i])
			count++;
	}

	/* only contemplate cloning if more than one connector is enabled */
	if (count <= 1)
		return false;

	/* check the command line or if nothing common pick 1024x768 */
	can_clone = true;
	for (i = 0; i < fb_helper->connector_count; i++) {
		if (!enabled[i])
			continue;
		fb_helper_conn = fb_helper->connector_info[i];
		modes[i] = drm_pick_cmdline_mode(fb_helper_conn, width, height);
		if (!modes[i]) {
			can_clone = false;
			break;
		}
		for (j = 0; j < i; j++) {
			if (!enabled[j])
				continue;
			if (!drm_mode_equal(modes[j], modes[i]))
				can_clone = false;
		}
	}

	if (can_clone) {
		DRM_DEBUG_KMS("can clone using command line\n");
		return true;
	}

	/* try and find a 1024x768 mode on each connector */
	can_clone = true;
	dmt_mode = drm_mode_find_dmt(fb_helper->dev, 1024, 768, 60, false);

	for (i = 0; i < fb_helper->connector_count; i++) {

		if (!enabled[i])
			continue;

		fb_helper_conn = fb_helper->connector_info[i];
		list_for_each_entry(mode, &fb_helper_conn->connector->modes, head) {
			if (drm_mode_equal(mode, dmt_mode))
				modes[i] = mode;
		}
		if (!modes[i])
			can_clone = false;
	}

	if (can_clone) {
		DRM_DEBUG_KMS("can clone using 1024x768\n");
		return true;
	}
	DRM_INFO("kms: can't enable cloning when we probably wanted to.\n");
	return false;
}

static int drm_get_tile_offsets(struct drm_fb_helper *fb_helper,
				struct drm_display_mode **modes,
				struct drm_fb_offset *offsets,
				int idx,
				int h_idx, int v_idx)
{
	struct drm_fb_helper_connector *fb_helper_conn;
	int i;
	int hoffset = 0, voffset = 0;

	for (i = 0; i < fb_helper->connector_count; i++) {
		fb_helper_conn = fb_helper->connector_info[i];
		if (!fb_helper_conn->connector->has_tile)
			continue;

		if (!modes[i] && (h_idx || v_idx)) {
			DRM_DEBUG_KMS("no modes for connector tiled %d %d\n", i,
				      fb_helper_conn->connector->base.id);
			continue;
		}
		if (fb_helper_conn->connector->tile_h_loc < h_idx)
			hoffset += modes[i]->hdisplay;

		if (fb_helper_conn->connector->tile_v_loc < v_idx)
			voffset += modes[i]->vdisplay;
	}
	offsets[idx].x = hoffset;
	offsets[idx].y = voffset;
	DRM_DEBUG_KMS("returned %d %d for %d %d\n", hoffset, voffset, h_idx, v_idx);
	return 0;
}

static bool drm_target_preferred(struct drm_fb_helper *fb_helper,
				 struct drm_display_mode **modes,
				 struct drm_fb_offset *offsets,
				 bool *enabled, int width, int height)
{
	struct drm_fb_helper_connector *fb_helper_conn;
	int i;
	uint64_t conn_configured = 0, mask;
	int tile_pass = 0;
	mask = (1 << fb_helper->connector_count) - 1;
retry:
	for (i = 0; i < fb_helper->connector_count; i++) {
		fb_helper_conn = fb_helper->connector_info[i];

		if (conn_configured & (1 << i))
			continue;

		if (enabled[i] == false) {
			conn_configured |= (1 << i);
			continue;
		}

		/* first pass over all the untiled connectors */
		if (tile_pass == 0 && fb_helper_conn->connector->has_tile)
			continue;

		if (tile_pass == 1) {
			if (fb_helper_conn->connector->tile_h_loc != 0 ||
			    fb_helper_conn->connector->tile_v_loc != 0)
				continue;

		} else {
			if (fb_helper_conn->connector->tile_h_loc != tile_pass -1 &&
			    fb_helper_conn->connector->tile_v_loc != tile_pass - 1)
			/* if this tile_pass doesn't cover any of the tiles - keep going */
				continue;

			/* find the tile offsets for this pass - need
			   to find all tiles left and above */
			drm_get_tile_offsets(fb_helper, modes, offsets,
					     i, fb_helper_conn->connector->tile_h_loc, fb_helper_conn->connector->tile_v_loc);
		}
		DRM_DEBUG_KMS("looking for cmdline mode on connector %d\n",
			      fb_helper_conn->connector->base.id);

		/* got for command line mode first */
		modes[i] = drm_pick_cmdline_mode(fb_helper_conn, width, height);
		if (!modes[i]) {
			DRM_DEBUG_KMS("looking for preferred mode on connector %d %d\n",
				      fb_helper_conn->connector->base.id, fb_helper_conn->connector->tile_group ? fb_helper_conn->connector->tile_group->id : 0);
			modes[i] = drm_has_preferred_mode(fb_helper_conn, width, height);
		}
		/* No preferred modes, pick one off the list */
		if (!modes[i] && !list_empty(&fb_helper_conn->connector->modes)) {
			list_for_each_entry(modes[i], &fb_helper_conn->connector->modes, head)
				break;
		}
		DRM_DEBUG_KMS("found mode %s\n", modes[i] ? modes[i]->name :
			  "none");
		conn_configured |= (1 << i);
	}

	if ((conn_configured & mask) != mask) {
		tile_pass++;
		goto retry;
	}
	return true;
}

static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
			  struct drm_fb_helper_crtc **best_crtcs,
			  struct drm_display_mode **modes,
			  int n, int width, int height)
{
	int c, o;
	struct drm_connector *connector;
	const struct drm_connector_helper_funcs *connector_funcs;
	struct drm_encoder *encoder;
	int my_score, best_score, score;
	struct drm_fb_helper_crtc **crtcs, *crtc;
	struct drm_fb_helper_connector *fb_helper_conn;

	if (n == fb_helper->connector_count)
		return 0;

	fb_helper_conn = fb_helper->connector_info[n];
	connector = fb_helper_conn->connector;

	best_crtcs[n] = NULL;
	best_score = drm_pick_crtcs(fb_helper, best_crtcs, modes, n+1, width, height);
	if (modes[n] == NULL)
		return best_score;

	crtcs = kzalloc(fb_helper->connector_count *
			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
	if (!crtcs)
		return best_score;

	my_score = 1;
	if (connector->status == connector_status_connected)
		my_score++;
	if (drm_has_cmdline_mode(fb_helper_conn))
		my_score++;
	if (drm_has_preferred_mode(fb_helper_conn, width, height))
		my_score++;

	connector_funcs = connector->helper_private;

	/*
	 * If the DRM device implements atomic hooks and ->best_encoder() is
	 * NULL we fallback to the default drm_atomic_helper_best_encoder()
	 * helper.
	 */
	if (fb_helper->dev->mode_config.funcs->atomic_commit &&
	    !connector_funcs->best_encoder)
		encoder = drm_atomic_helper_best_encoder(connector);
	else
		encoder = connector_funcs->best_encoder(connector);

	if (!encoder)
		goto out;

	/* select a crtc for this connector and then attempt to configure
	   remaining connectors */
	for (c = 0; c < fb_helper->crtc_count; c++) {
		crtc = &fb_helper->crtc_info[c];

		if ((encoder->possible_crtcs & (1 << c)) == 0)
			continue;

		for (o = 0; o < n; o++)
			if (best_crtcs[o] == crtc)
				break;

		if (o < n) {
			/* ignore cloning unless only a single crtc */
			if (fb_helper->crtc_count > 1)
				continue;

			if (!drm_mode_equal(modes[o], modes[n]))
				continue;
		}

		crtcs[n] = crtc;
		memcpy(crtcs, best_crtcs, n * sizeof(struct drm_fb_helper_crtc *));
		score = my_score + drm_pick_crtcs(fb_helper, crtcs, modes, n + 1,
						  width, height);
		if (score > best_score) {
			best_score = score;
			memcpy(best_crtcs, crtcs,
			       fb_helper->connector_count *
			       sizeof(struct drm_fb_helper_crtc *));
		}
	}
out:
	kfree(crtcs);
	return best_score;
}

static void drm_setup_crtcs(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	struct drm_fb_helper_crtc **crtcs;
	struct drm_display_mode **modes;
	struct drm_fb_offset *offsets;
	bool *enabled;
	int width, height;
	int i;

	DRM_DEBUG_KMS("\n");

	width = dev->mode_config.max_width;
	height = dev->mode_config.max_height;

	crtcs = kcalloc(fb_helper->connector_count,
			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
	modes = kcalloc(fb_helper->connector_count,
			sizeof(struct drm_display_mode *), GFP_KERNEL);
	offsets = kcalloc(fb_helper->connector_count,
			  sizeof(struct drm_fb_offset), GFP_KERNEL);
	enabled = kcalloc(fb_helper->connector_count,
			  sizeof(bool), GFP_KERNEL);
	if (!crtcs || !modes || !enabled || !offsets) {
		DRM_ERROR("Memory allocation failed\n");
		goto out;
	}


	drm_enable_connectors(fb_helper, enabled);

	if (!(fb_helper->funcs->initial_config &&
	      fb_helper->funcs->initial_config(fb_helper, crtcs, modes,
					       offsets,
					       enabled, width, height))) {
		memset(modes, 0, fb_helper->connector_count*sizeof(modes[0]));
		memset(crtcs, 0, fb_helper->connector_count*sizeof(crtcs[0]));
		memset(offsets, 0, fb_helper->connector_count*sizeof(offsets[0]));

		if (!drm_target_cloned(fb_helper, modes, offsets,
				       enabled, width, height) &&
		    !drm_target_preferred(fb_helper, modes, offsets,
					  enabled, width, height))
			DRM_ERROR("Unable to find initial modes\n");

		DRM_DEBUG_KMS("picking CRTCs for %dx%d config\n",
			      width, height);

		drm_pick_crtcs(fb_helper, crtcs, modes, 0, width, height);
	}

	/* need to set the modesets up here for use later */
	/* fill out the connector<->crtc mappings into the modesets */
	for (i = 0; i < fb_helper->crtc_count; i++)
		drm_fb_helper_modeset_release(fb_helper,
					      &fb_helper->crtc_info[i].mode_set);

	for (i = 0; i < fb_helper->connector_count; i++) {
		struct drm_display_mode *mode = modes[i];
		struct drm_fb_helper_crtc *fb_crtc = crtcs[i];
		struct drm_fb_offset *offset = &offsets[i];
		struct drm_mode_set *modeset = &fb_crtc->mode_set;

		if (mode && fb_crtc) {
			struct drm_connector *connector =
				fb_helper->connector_info[i]->connector;

			DRM_DEBUG_KMS("desired mode %s set on crtc %d (%d,%d)\n",
				      mode->name, fb_crtc->mode_set.crtc->base.id, offset->x, offset->y);

			fb_crtc->desired_mode = mode;
			fb_crtc->x = offset->x;
			fb_crtc->y = offset->y;
			modeset->mode = drm_mode_duplicate(dev,
							   fb_crtc->desired_mode);
			drm_connector_reference(connector);
			modeset->connectors[modeset->num_connectors++] = connector;
			modeset->fb = fb_helper->fb;
			modeset->x = offset->x;
			modeset->y = offset->y;
		}
	}
out:
	kfree(crtcs);
	kfree(modes);
	kfree(offsets);
	kfree(enabled);
}

/**
 * drm_fb_helper_initial_config - setup a sane initial connector configuration
 * @fb_helper: fb_helper device struct
 * @bpp_sel: bpp value to use for the framebuffer configuration
 *
 * Scans the CRTCs and connectors and tries to put together an initial setup.
 * At the moment, this is a cloned configuration across all heads with
 * a new framebuffer object as the backing store.
 *
 * Note that this also registers the fbdev and so allows userspace to call into
 * the driver through the fbdev interfaces.
 *
 * This function will call down into the ->fb_probe callback to let
 * the driver allocate and initialize the fbdev info structure and the drm
 * framebuffer used to back the fbdev. drm_fb_helper_fill_var() and
 * drm_fb_helper_fill_fix() are provided as helpers to setup simple default
 * values for the fbdev info structure.
 *
 * HANG DEBUGGING:
 *
 * When you have fbcon support built-in or already loaded, this function will do
 * a full modeset to setup the fbdev console. Due to locking misdesign in the
 * VT/fbdev subsystem that entire modeset sequence has to be done while holding
 * console_lock. Until console_unlock is called no dmesg lines will be sent out
 * to consoles, not even serial console. This means when your driver crashes,
 * you will see absolutely nothing else but a system stuck in this function,
 * with no further output. Any kind of printk() you place within your own driver
 * or in the drm core modeset code will also never show up.
 *
 * Standard debug practice is to run the fbcon setup without taking the
 * console_lock as a hack, to be able to see backtraces and crashes on the
 * serial line. This can be done by setting the fb.lockless_register_fb=1 kernel
 * cmdline option.
 *
 * The other option is to just disable fbdev emulation since very likely the
 * first modeset from userspace will crash in the same way, and is even easier
 * to debug. This can be done by setting the drm_kms_helper.fbdev_emulation=0
 * kernel cmdline option.
 *
 * RETURNS:
 * Zero if everything went ok, nonzero otherwise.
 */
int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
{
	struct drm_device *dev = fb_helper->dev;
	int count = 0;

	if (!drm_fbdev_emulation)
		return 0;

	mutex_lock(&dev->mode_config.mutex);
	count = drm_fb_helper_probe_connector_modes(fb_helper,
						    dev->mode_config.max_width,
						    dev->mode_config.max_height);
	mutex_unlock(&dev->mode_config.mutex);
	/*
	 * we shouldn't end up with no modes here.
	 */
	if (count == 0)
		dev_info(fb_helper->dev->dev, "No connectors reported connected with modes\n");

	drm_setup_crtcs(fb_helper);

	return drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
}
EXPORT_SYMBOL(drm_fb_helper_initial_config);

/**
 * drm_fb_helper_hotplug_event - respond to a hotplug notification by
 *                               probing all the outputs attached to the fb
 * @fb_helper: the drm_fb_helper
 *
 * Scan the connectors attached to the fb_helper and try to put together a
 * setup after notification of a change in output configuration.
 *
 * Called at runtime, takes the mode config locks to be able to check/change the
 * modeset configuration. Must be run from process context (which usually means
 * either the output polling work or a work item launched from the driver's
 * hotplug interrupt).
 *
 * Note that drivers may call this even before calling
 * drm_fb_helper_initial_config but only after drm_fb_helper_init. This allows
 * for a race-free fbcon setup and will make sure that the fbdev emulation will
 * not miss any hotplug events.
 *
 * RETURNS:
 * 0 on success and a non-zero error code otherwise.
 */
int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper)
{
	struct drm_device *dev = fb_helper->dev;
	u32 max_width, max_height;

	if (!drm_fbdev_emulation)
		return 0;

	mutex_lock(&fb_helper->dev->mode_config.mutex);
	if (!fb_helper->fb || !drm_fb_helper_is_bound(fb_helper)) {
		fb_helper->delayed_hotplug = true;
		mutex_unlock(&fb_helper->dev->mode_config.mutex);
		return 0;
	}
	DRM_DEBUG_KMS("\n");

	max_width = fb_helper->fb->width;
	max_height = fb_helper->fb->height;

	drm_fb_helper_probe_connector_modes(fb_helper, max_width, max_height);
	mutex_unlock(&fb_helper->dev->mode_config.mutex);

	drm_modeset_lock_all(dev);
	drm_setup_crtcs(fb_helper);
	drm_modeset_unlock_all(dev);
	drm_fb_helper_set_par(fb_helper->fbdev);

	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_hotplug_event);

/* The Kconfig DRM_KMS_HELPER selects FRAMEBUFFER_CONSOLE (if !EXPERT)
 * but the module doesn't depend on any fb console symbols.  At least
 * attempt to load fbcon to avoid leaving the system without a usable console.
 */
int __init drm_fb_helper_modinit(void)
{
#if defined(CONFIG_FRAMEBUFFER_CONSOLE_MODULE) && !defined(CONFIG_EXPERT)
	const char *name = "fbcon";
	struct module *fbcon;

	mutex_lock(&module_mutex);
	fbcon = find_module(name);
	mutex_unlock(&module_mutex);

	if (!fbcon)
		request_module_nowait(name);
#endif
	return 0;
}
EXPORT_SYMBOL(drm_fb_helper_modinit);