drivers/gpu/drm/i915/i915_gem_gtt.c

/*
 * Copyright © 2010 Daniel Vetter
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 */

#include <drm/drmP.h>
#include <drm/i915_drm.h>
#include "i915_drv.h"
#include "i915_trace.h"
#include "intel_drv.h"

typedef uint32_t gen6_gtt_pte_t;

/* PPGTT stuff */
#define GEN6_GTT_ADDR_ENCODE(addr)	((addr) | (((addr) >> 28) & 0xff0))

#define GEN6_PDE_VALID			(1 << 0)
/* gen6+ has bit 11-4 for physical addr bit 39-32 */
#define GEN6_PDE_ADDR_ENCODE(addr)	GEN6_GTT_ADDR_ENCODE(addr)

#define GEN6_PTE_VALID			(1 << 0)
#define GEN6_PTE_UNCACHED		(1 << 1)
#define HSW_PTE_UNCACHED		(0)
#define GEN6_PTE_CACHE_LLC		(2 << 1)
#define GEN6_PTE_CACHE_LLC_MLC		(3 << 1)
#define GEN6_PTE_ADDR_ENCODE(addr)	GEN6_GTT_ADDR_ENCODE(addr)

static inline gen6_gtt_pte_t gen6_pte_encode(struct drm_device *dev,
					dma_addr_t addr,
					enum i915_cache_level level)
{
	gen6_gtt_pte_t pte = GEN6_PTE_VALID;
	pte |= GEN6_PTE_ADDR_ENCODE(addr);

	switch (level) {
	case I915_CACHE_LLC_MLC:
		/* Haswell doesn't set L3 this way */
		if (IS_HASWELL(dev))
			pte |= GEN6_PTE_CACHE_LLC;
		else
			pte |= GEN6_PTE_CACHE_LLC_MLC;
		break;
	case I915_CACHE_LLC:
		pte |= GEN6_PTE_CACHE_LLC;
		break;
	case I915_CACHE_NONE:
		if (IS_HASWELL(dev))
			pte |= HSW_PTE_UNCACHED;
		else
			pte |= GEN6_PTE_UNCACHED;
		break;
	default:
		BUG();
	}

	return pte;
}

/* PPGTT support for Sandybdrige/Gen6 and later */
static void gen6_ppgtt_clear_range(struct i915_hw_ppgtt *ppgtt,
				   unsigned first_entry,
				   unsigned num_entries)
{
	gen6_gtt_pte_t *pt_vaddr, scratch_pte;
	unsigned act_pt = first_entry / I915_PPGTT_PT_ENTRIES;
	unsigned first_pte = first_entry % I915_PPGTT_PT_ENTRIES;
	unsigned last_pte, i;

	scratch_pte = gen6_pte_encode(ppgtt->dev,
				      ppgtt->scratch_page_dma_addr,
				      I915_CACHE_LLC);

	while (num_entries) {
		last_pte = first_pte + num_entries;
		if (last_pte > I915_PPGTT_PT_ENTRIES)
			last_pte = I915_PPGTT_PT_ENTRIES;

		pt_vaddr = kmap_atomic(ppgtt->pt_pages[act_pt]);

		for (i = first_pte; i < last_pte; i++)
			pt_vaddr[i] = scratch_pte;

		kunmap_atomic(pt_vaddr);

		num_entries -= last_pte - first_pte;
		first_pte = 0;
		act_pt++;
	}
}

static void gen6_ppgtt_insert_entries(struct i915_hw_ppgtt *ppgtt,
				      struct sg_table *pages,
				      unsigned first_entry,
				      enum i915_cache_level cache_level)
{
	gen6_gtt_pte_t *pt_vaddr;
	unsigned act_pt = first_entry / I915_PPGTT_PT_ENTRIES;
	unsigned act_pte = first_entry % I915_PPGTT_PT_ENTRIES;
	struct sg_page_iter sg_iter;

	pt_vaddr = kmap_atomic(ppgtt->pt_pages[act_pt]);
	for_each_sg_page(pages->sgl, &sg_iter, pages->nents, 0) {
		dma_addr_t page_addr;

		page_addr = sg_page_iter_dma_address(&sg_iter);
		pt_vaddr[act_pte] = gen6_pte_encode(ppgtt->dev, page_addr,
						    cache_level);
		if (++act_pte == I915_PPGTT_PT_ENTRIES) {
			kunmap_atomic(pt_vaddr);
			act_pt++;
			pt_vaddr = kmap_atomic(ppgtt->pt_pages[act_pt]);
			act_pte = 0;

		}
	}
	kunmap_atomic(pt_vaddr);
}

static void gen6_ppgtt_cleanup(struct i915_hw_ppgtt *ppgtt)
{
	int i;

	if (ppgtt->pt_dma_addr) {
		for (i = 0; i < ppgtt->num_pd_entries; i++)
			pci_unmap_page(ppgtt->dev->pdev,
				       ppgtt->pt_dma_addr[i],
				       4096, PCI_DMA_BIDIRECTIONAL);
	}

	kfree(ppgtt->pt_dma_addr);
	for (i = 0; i < ppgtt->num_pd_entries; i++)
		__free_page(ppgtt->pt_pages[i]);
	kfree(ppgtt->pt_pages);
	kfree(ppgtt);
}

static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
{
	struct drm_device *dev = ppgtt->dev;
	struct drm_i915_private *dev_priv = dev->dev_private;
	unsigned first_pd_entry_in_global_pt;
	int i;
	int ret = -ENOMEM;

	/* ppgtt PDEs reside in the global gtt pagetable, which has 512*1024
	 * entries. For aliasing ppgtt support we just steal them at the end for
	 * now. */
	first_pd_entry_in_global_pt =
		gtt_total_entries(dev_priv->gtt) - I915_PPGTT_PD_ENTRIES;

	ppgtt->num_pd_entries = I915_PPGTT_PD_ENTRIES;
	ppgtt->clear_range = gen6_ppgtt_clear_range;
	ppgtt->insert_entries = gen6_ppgtt_insert_entries;
	ppgtt->cleanup = gen6_ppgtt_cleanup;
	ppgtt->pt_pages = kzalloc(sizeof(struct page *)*ppgtt->num_pd_entries,
				  GFP_KERNEL);
	if (!ppgtt->pt_pages)
		return -ENOMEM;

	for (i = 0; i < ppgtt->num_pd_entries; i++) {
		ppgtt->pt_pages[i] = alloc_page(GFP_KERNEL);
		if (!ppgtt->pt_pages[i])
			goto err_pt_alloc;
	}

	ppgtt->pt_dma_addr = kzalloc(sizeof(dma_addr_t) *ppgtt->num_pd_entries,
				     GFP_KERNEL);
	if (!ppgtt->pt_dma_addr)
		goto err_pt_alloc;

	for (i = 0; i < ppgtt->num_pd_entries; i++) {
		dma_addr_t pt_addr;

		pt_addr = pci_map_page(dev->pdev, ppgtt->pt_pages[i], 0, 4096,
				       PCI_DMA_BIDIRECTIONAL);

		if (pci_dma_mapping_error(dev->pdev, pt_addr)) {
			ret = -EIO;
			goto err_pd_pin;

		}
		ppgtt->pt_dma_addr[i] = pt_addr;
	}

	ppgtt->scratch_page_dma_addr = dev_priv->gtt.scratch_page_dma;

	ppgtt->clear_range(ppgtt, 0,
			   ppgtt->num_pd_entries*I915_PPGTT_PT_ENTRIES);

	ppgtt->pd_offset = first_pd_entry_in_global_pt * sizeof(gen6_gtt_pte_t);

	return 0;

err_pd_pin:
	if (ppgtt->pt_dma_addr) {
		for (i--; i >= 0; i--)
			pci_unmap_page(dev->pdev, ppgtt->pt_dma_addr[i],
				       4096, PCI_DMA_BIDIRECTIONAL);
	}
err_pt_alloc:
	kfree(ppgtt->pt_dma_addr);
	for (i = 0; i < ppgtt->num_pd_entries; i++) {
		if (ppgtt->pt_pages[i])
			__free_page(ppgtt->pt_pages[i]);
	}
	kfree(ppgtt->pt_pages);

	return ret;
}

static int i915_gem_init_aliasing_ppgtt(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct i915_hw_ppgtt *ppgtt;
	int ret;

	ppgtt = kzalloc(sizeof(*ppgtt), GFP_KERNEL);
	if (!ppgtt)
		return -ENOMEM;

	ppgtt->dev = dev;

	ret = gen6_ppgtt_init(ppgtt);
	if (ret)
		kfree(ppgtt);
	else
		dev_priv->mm.aliasing_ppgtt = ppgtt;

	return ret;
}

void i915_gem_cleanup_aliasing_ppgtt(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct i915_hw_ppgtt *ppgtt = dev_priv->mm.aliasing_ppgtt;

	if (!ppgtt)
		return;

	ppgtt->cleanup(ppgtt);
}

void i915_ppgtt_bind_object(struct i915_hw_ppgtt *ppgtt,
			    struct drm_i915_gem_object *obj,
			    enum i915_cache_level cache_level)
{
	ppgtt->insert_entries(ppgtt, obj->pages,
			      obj->gtt_space->start >> PAGE_SHIFT,
			      cache_level);
}

void i915_ppgtt_unbind_object(struct i915_hw_ppgtt *ppgtt,
			      struct drm_i915_gem_object *obj)
{
	ppgtt->clear_range(ppgtt,
			   obj->gtt_space->start >> PAGE_SHIFT,
			   obj->base.size >> PAGE_SHIFT);
}

void i915_gem_init_ppgtt(struct drm_device *dev)
{
	drm_i915_private_t *dev_priv = dev->dev_private;
	uint32_t pd_offset;
	struct intel_ring_buffer *ring;
	struct i915_hw_ppgtt *ppgtt = dev_priv->mm.aliasing_ppgtt;
	gen6_gtt_pte_t __iomem *pd_addr;
	uint32_t pd_entry;
	int i;

	if (!dev_priv->mm.aliasing_ppgtt)
		return;


	pd_addr = (gen6_gtt_pte_t __iomem *)dev_priv->gtt.gsm +
		ppgtt->pd_offset / sizeof(gen6_gtt_pte_t);
	for (i = 0; i < ppgtt->num_pd_entries; i++) {
		dma_addr_t pt_addr;

		pt_addr = ppgtt->pt_dma_addr[i];
		pd_entry = GEN6_PDE_ADDR_ENCODE(pt_addr);
		pd_entry |= GEN6_PDE_VALID;

		writel(pd_entry, pd_addr + i);
	}
	readl(pd_addr);

	pd_offset = ppgtt->pd_offset;
	pd_offset /= 64; /* in cachelines, */
	pd_offset <<= 16;

	if (INTEL_INFO(dev)->gen == 6) {
		uint32_t ecochk, gab_ctl, ecobits;

		ecobits = I915_READ(GAC_ECO_BITS);
		I915_WRITE(GAC_ECO_BITS, ecobits | ECOBITS_PPGTT_CACHE64B);

		gab_ctl = I915_READ(GAB_CTL);
		I915_WRITE(GAB_CTL, gab_ctl | GAB_CTL_CONT_AFTER_PAGEFAULT);

		ecochk = I915_READ(GAM_ECOCHK);
		I915_WRITE(GAM_ECOCHK, ecochk | ECOCHK_SNB_BIT |
				       ECOCHK_PPGTT_CACHE64B);
		I915_WRITE(GFX_MODE, _MASKED_BIT_ENABLE(GFX_PPGTT_ENABLE));
	} else if (INTEL_INFO(dev)->gen >= 7) {
		I915_WRITE(GAM_ECOCHK, ECOCHK_PPGTT_CACHE64B);
		/* GFX_MODE is per-ring on gen7+ */
	}

	for_each_ring(ring, dev_priv, i) {
		if (INTEL_INFO(dev)->gen >= 7)
			I915_WRITE(RING_MODE_GEN7(ring),
				   _MASKED_BIT_ENABLE(GFX_PPGTT_ENABLE));

		I915_WRITE(RING_PP_DIR_DCLV(ring), PP_DIR_DCLV_2G);
		I915_WRITE(RING_PP_DIR_BASE(ring), pd_offset);
	}
}

extern int intel_iommu_gfx_mapped;
/* Certain Gen5 chipsets require require idling the GPU before
 * unmapping anything from the GTT when VT-d is enabled.
 */
static inline bool needs_idle_maps(struct drm_device *dev)
{
#ifdef CONFIG_INTEL_IOMMU
	/* Query intel_iommu to see if we need the workaround. Presumably that
	 * was loaded first.
	 */
	if (IS_GEN5(dev) && IS_MOBILE(dev) && intel_iommu_gfx_mapped)
		return true;
#endif
	return false;
}

static bool do_idling(struct drm_i915_private *dev_priv)
{
	bool ret = dev_priv->mm.interruptible;

	if (unlikely(dev_priv->gtt.do_idle_maps)) {
		dev_priv->mm.interruptible = false;
		if (i915_gpu_idle(dev_priv->dev)) {
			DRM_ERROR("Couldn't idle GPU\n");
			/* Wait a bit, in hopes it avoids the hang */
			udelay(10);
		}
	}

	return ret;
}

static void undo_idling(struct drm_i915_private *dev_priv, bool interruptible)
{
	if (unlikely(dev_priv->gtt.do_idle_maps))
		dev_priv->mm.interruptible = interruptible;
}

void i915_gem_restore_gtt_mappings(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct drm_i915_gem_object *obj;

	/* First fill our portion of the GTT with scratch pages */
	dev_priv->gtt.gtt_clear_range(dev, dev_priv->gtt.start / PAGE_SIZE,
				      dev_priv->gtt.total / PAGE_SIZE);

	list_for_each_entry(obj, &dev_priv->mm.bound_list, gtt_list) {
		i915_gem_clflush_object(obj);
		i915_gem_gtt_bind_object(obj, obj->cache_level);
	}

	i915_gem_chipset_flush(dev);
}

int i915_gem_gtt_prepare_object(struct drm_i915_gem_object *obj)
{
	if (obj->has_dma_mapping)
		return 0;

	if (!dma_map_sg(&obj->base.dev->pdev->dev,
			obj->pages->sgl, obj->pages->nents,
			PCI_DMA_BIDIRECTIONAL))
		return -ENOSPC;

	return 0;
}

/*
 * Binds an object into the global gtt with the specified cache level. The object
 * will be accessible to the GPU via commands whose operands reference offsets
 * within the global GTT as well as accessible by the GPU through the GMADR
 * mapped BAR (dev_priv->mm.gtt->gtt).
 */
static void gen6_ggtt_insert_entries(struct drm_device *dev,
				     struct sg_table *st,
				     unsigned int first_entry,
				     enum i915_cache_level level)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	gen6_gtt_pte_t __iomem *gtt_entries =
		(gen6_gtt_pte_t __iomem *)dev_priv->gtt.gsm + first_entry;
	int i = 0;
	struct sg_page_iter sg_iter;
	dma_addr_t addr;

	for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
		addr = sg_page_iter_dma_address(&sg_iter);
		iowrite32(gen6_pte_encode(dev, addr, level), &gtt_entries[i]);
		i++;
	}

	/* XXX: This serves as a posting read to make sure that the PTE has
	 * actually been updated. There is some concern that even though
	 * registers and PTEs are within the same BAR that they are potentially
	 * of NUMA access patterns. Therefore, even with the way we assume
	 * hardware should work, we must keep this posting read for paranoia.
	 */
	if (i != 0)
		WARN_ON(readl(&gtt_entries[i-1])
			!= gen6_pte_encode(dev, addr, level));

	/* This next bit makes the above posting read even more important. We
	 * want to flush the TLBs only after we're certain all the PTE updates
	 * have finished.
	 */
	I915_WRITE(GFX_FLSH_CNTL_GEN6, GFX_FLSH_CNTL_EN);
	POSTING_READ(GFX_FLSH_CNTL_GEN6);
}

static void gen6_ggtt_clear_range(struct drm_device *dev,
				  unsigned int first_entry,
				  unsigned int num_entries)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	gen6_gtt_pte_t scratch_pte, __iomem *gtt_base =
		(gen6_gtt_pte_t __iomem *) dev_priv->gtt.gsm + first_entry;
	const int max_entries = gtt_total_entries(dev_priv->gtt) - first_entry;
	int i;

	if (WARN(num_entries > max_entries,
		 "First entry = %d; Num entries = %d (max=%d)\n",
		 first_entry, num_entries, max_entries))
		num_entries = max_entries;

	scratch_pte = gen6_pte_encode(dev, dev_priv->gtt.scratch_page_dma,
				      I915_CACHE_LLC);
	for (i = 0; i < num_entries; i++)
		iowrite32(scratch_pte, &gtt_base[i]);
	readl(gtt_base);
}


static void i915_ggtt_insert_entries(struct drm_device *dev,
				     struct sg_table *st,
				     unsigned int pg_start,
				     enum i915_cache_level cache_level)
{
	unsigned int flags = (cache_level == I915_CACHE_NONE) ?
		AGP_USER_MEMORY : AGP_USER_CACHED_MEMORY;

	intel_gtt_insert_sg_entries(st, pg_start, flags);

}

static void i915_ggtt_clear_range(struct drm_device *dev,
				  unsigned int first_entry,
				  unsigned int num_entries)
{
	intel_gtt_clear_range(first_entry, num_entries);
}


void i915_gem_gtt_bind_object(struct drm_i915_gem_object *obj,
			      enum i915_cache_level cache_level)
{
	struct drm_device *dev = obj->base.dev;
	struct drm_i915_private *dev_priv = dev->dev_private;

	dev_priv->gtt.gtt_insert_entries(dev, obj->pages,
					 obj->gtt_space->start >> PAGE_SHIFT,
					 cache_level);

	obj->has_global_gtt_mapping = 1;
}

void i915_gem_gtt_unbind_object(struct drm_i915_gem_object *obj)
{
	struct drm_device *dev = obj->base.dev;
	struct drm_i915_private *dev_priv = dev->dev_private;

	dev_priv->gtt.gtt_clear_range(obj->base.dev,
				      obj->gtt_space->start >> PAGE_SHIFT,
				      obj->base.size >> PAGE_SHIFT);

	obj->has_global_gtt_mapping = 0;
}

void i915_gem_gtt_finish_object(struct drm_i915_gem_object *obj)
{
	struct drm_device *dev = obj->base.dev;
	struct drm_i915_private *dev_priv = dev->dev_private;
	bool interruptible;

	interruptible = do_idling(dev_priv);

	if (!obj->has_dma_mapping)
		dma_unmap_sg(&dev->pdev->dev,
			     obj->pages->sgl, obj->pages->nents,
			     PCI_DMA_BIDIRECTIONAL);

	undo_idling(dev_priv, interruptible);
}

static void i915_gtt_color_adjust(struct drm_mm_node *node,
				  unsigned long color,
				  unsigned long *start,
				  unsigned long *end)
{
	if (node->color != color)
		*start += 4096;

	if (!list_empty(&node->node_list)) {
		node = list_entry(node->node_list.next,
				  struct drm_mm_node,
				  node_list);
		if (node->allocated && node->color != color)
			*end -= 4096;
	}
}
void i915_gem_setup_global_gtt(struct drm_device *dev,
			       unsigned long start,
			       unsigned long mappable_end,
			       unsigned long end)
{
	/* Let GEM Manage all of the aperture.
	 *
	 * However, leave one page at the end still bound to the scratch page.
	 * There are a number of places where the hardware apparently prefetches
	 * past the end of the object, and we've seen multiple hangs with the
	 * GPU head pointer stuck in a batchbuffer bound at the last page of the
	 * aperture.  One page should be enough to keep any prefetching inside
	 * of the aperture.
	 */
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct drm_mm_node *entry;
	struct drm_i915_gem_object *obj;
	unsigned long hole_start, hole_end;

	BUG_ON(mappable_end > end);

	/* Subtract the guard page ... */
	drm_mm_init(&dev_priv->mm.gtt_space, start, end - start - PAGE_SIZE);
	if (!HAS_LLC(dev))
		dev_priv->mm.gtt_space.color_adjust = i915_gtt_color_adjust;

	/* Mark any preallocated objects as occupied */
	list_for_each_entry(obj, &dev_priv->mm.bound_list, gtt_list) {
		DRM_DEBUG_KMS("reserving preallocated space: %x + %zx\n",
			      obj->gtt_offset, obj->base.size);

		BUG_ON(obj->gtt_space != I915_GTT_RESERVED);
		obj->gtt_space = drm_mm_create_block(&dev_priv->mm.gtt_space,
						     obj->gtt_offset,
						     obj->base.size,
						     false);
		obj->has_global_gtt_mapping = 1;
	}

	dev_priv->gtt.start = start;
	dev_priv->gtt.total = end - start;

	/* Clear any non-preallocated blocks */
	drm_mm_for_each_hole(entry, &dev_priv->mm.gtt_space,
			     hole_start, hole_end) {
		DRM_DEBUG_KMS("clearing unused GTT space: [%lx, %lx]\n",
			      hole_start, hole_end);
		dev_priv->gtt.gtt_clear_range(dev, hole_start / PAGE_SIZE,
					      (hole_end-hole_start) / PAGE_SIZE);
	}

	/* And finally clear the reserved guard page */
	dev_priv->gtt.gtt_clear_range(dev, end / PAGE_SIZE - 1, 1);
}

static bool
intel_enable_ppgtt(struct drm_device *dev)
{
	if (i915_enable_ppgtt >= 0)
		return i915_enable_ppgtt;

#ifdef CONFIG_INTEL_IOMMU
	/* Disable ppgtt on SNB if VT-d is on. */
	if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped)
		return false;
#endif

	return true;
}

void i915_gem_init_global_gtt(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	unsigned long gtt_size, mappable_size;

	gtt_size = dev_priv->gtt.total;
	mappable_size = dev_priv->gtt.mappable_end;

	if (intel_enable_ppgtt(dev) && HAS_ALIASING_PPGTT(dev)) {
		int ret;
		/* PPGTT pdes are stolen from global gtt ptes, so shrink the
		 * aperture accordingly when using aliasing ppgtt. */
		gtt_size -= I915_PPGTT_PD_ENTRIES*PAGE_SIZE;

		i915_gem_setup_global_gtt(dev, 0, mappable_size, gtt_size);

		ret = i915_gem_init_aliasing_ppgtt(dev);
		if (!ret)
			return;

		DRM_ERROR("Aliased PPGTT setup failed %d\n", ret);
		drm_mm_takedown(&dev_priv->mm.gtt_space);
		gtt_size += I915_PPGTT_PD_ENTRIES*PAGE_SIZE;
	}
	i915_gem_setup_global_gtt(dev, 0, mappable_size, gtt_size);
}

static int setup_scratch_page(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct page *page;
	dma_addr_t dma_addr;

	page = alloc_page(GFP_KERNEL | GFP_DMA32 | __GFP_ZERO);
	if (page == NULL)
		return -ENOMEM;
	get_page(page);
	set_pages_uc(page, 1);

#ifdef CONFIG_INTEL_IOMMU
	dma_addr = pci_map_page(dev->pdev, page, 0, PAGE_SIZE,
				PCI_DMA_BIDIRECTIONAL);
	if (pci_dma_mapping_error(dev->pdev, dma_addr))
		return -EINVAL;
#else
	dma_addr = page_to_phys(page);
#endif
	dev_priv->gtt.scratch_page = page;
	dev_priv->gtt.scratch_page_dma = dma_addr;

	return 0;
}

static void teardown_scratch_page(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	set_pages_wb(dev_priv->gtt.scratch_page, 1);
	pci_unmap_page(dev->pdev, dev_priv->gtt.scratch_page_dma,
		       PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
	put_page(dev_priv->gtt.scratch_page);
	__free_page(dev_priv->gtt.scratch_page);
}

static inline unsigned int gen6_get_total_gtt_size(u16 snb_gmch_ctl)
{
	snb_gmch_ctl >>= SNB_GMCH_GGMS_SHIFT;
	snb_gmch_ctl &= SNB_GMCH_GGMS_MASK;
	return snb_gmch_ctl << 20;
}

static inline size_t gen6_get_stolen_size(u16 snb_gmch_ctl)
{
	snb_gmch_ctl >>= SNB_GMCH_GMS_SHIFT;
	snb_gmch_ctl &= SNB_GMCH_GMS_MASK;
	return snb_gmch_ctl << 25; /* 32 MB units */
}

static inline size_t gen7_get_stolen_size(u16 snb_gmch_ctl)
{
	static const int stolen_decoder[] = {
		0, 0, 0, 0, 0, 32, 48, 64, 128, 256, 96, 160, 224, 352};
	snb_gmch_ctl >>= IVB_GMCH_GMS_SHIFT;
	snb_gmch_ctl &= IVB_GMCH_GMS_MASK;
	return stolen_decoder[snb_gmch_ctl] << 20;
}

static int gen6_gmch_probe(struct drm_device *dev,
			   size_t *gtt_total,
			   size_t *stolen,
			   phys_addr_t *mappable_base,
			   unsigned long *mappable_end)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	phys_addr_t gtt_bus_addr;
	unsigned int gtt_size;
	u16 snb_gmch_ctl;
	int ret;

	*mappable_base = pci_resource_start(dev->pdev, 2);
	*mappable_end = pci_resource_len(dev->pdev, 2);

	/* 64/512MB is the current min/max we actually know of, but this is just
	 * a coarse sanity check.
	 */
	if ((*mappable_end < (64<<20) || (*mappable_end > (512<<20)))) {
		DRM_ERROR("Unknown GMADR size (%lx)\n",
			  dev_priv->gtt.mappable_end);
		return -ENXIO;
	}

	if (!pci_set_dma_mask(dev->pdev, DMA_BIT_MASK(40)))
		pci_set_consistent_dma_mask(dev->pdev, DMA_BIT_MASK(40));
	pci_read_config_word(dev->pdev, SNB_GMCH_CTRL, &snb_gmch_ctl);
	gtt_size = gen6_get_total_gtt_size(snb_gmch_ctl);

	if (IS_GEN7(dev) && !IS_VALLEYVIEW(dev))
		*stolen = gen7_get_stolen_size(snb_gmch_ctl);
	else
		*stolen = gen6_get_stolen_size(snb_gmch_ctl);

	*gtt_total = (gtt_size / sizeof(gen6_gtt_pte_t)) << PAGE_SHIFT;

	/* For Modern GENs the PTEs and register space are split in the BAR */
	gtt_bus_addr = pci_resource_start(dev->pdev, 0) +
		(pci_resource_len(dev->pdev, 0) / 2);

	dev_priv->gtt.gsm = ioremap_wc(gtt_bus_addr, gtt_size);
	if (!dev_priv->gtt.gsm) {
		DRM_ERROR("Failed to map the gtt page table\n");
		return -ENOMEM;
	}

	ret = setup_scratch_page(dev);
	if (ret)
		DRM_ERROR("Scratch setup failed\n");

	dev_priv->gtt.gtt_clear_range = gen6_ggtt_clear_range;
	dev_priv->gtt.gtt_insert_entries = gen6_ggtt_insert_entries;

	return ret;
}

static void gen6_gmch_remove(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	iounmap(dev_priv->gtt.gsm);
	teardown_scratch_page(dev_priv->dev);
}

static int i915_gmch_probe(struct drm_device *dev,
			   size_t *gtt_total,
			   size_t *stolen,
			   phys_addr_t *mappable_base,
			   unsigned long *mappable_end)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	int ret;

	ret = intel_gmch_probe(dev_priv->bridge_dev, dev_priv->dev->pdev, NULL);
	if (!ret) {
		DRM_ERROR("failed to set up gmch\n");
		return -EIO;
	}

	intel_gtt_get(gtt_total, stolen, mappable_base, mappable_end);

	dev_priv->gtt.do_idle_maps = needs_idle_maps(dev_priv->dev);
	dev_priv->gtt.gtt_clear_range = i915_ggtt_clear_range;
	dev_priv->gtt.gtt_insert_entries = i915_ggtt_insert_entries;

	return 0;
}

static void i915_gmch_remove(struct drm_device *dev)
{
	intel_gmch_remove();
}

int i915_gem_gtt_init(struct drm_device *dev)
{
	struct drm_i915_private *dev_priv = dev->dev_private;
	struct i915_gtt *gtt = &dev_priv->gtt;
	unsigned long gtt_size;
	int ret;

	if (INTEL_INFO(dev)->gen <= 5) {
		dev_priv->gtt.gtt_probe = i915_gmch_probe;
		dev_priv->gtt.gtt_remove = i915_gmch_remove;
	} else {
		dev_priv->gtt.gtt_probe = gen6_gmch_probe;
		dev_priv->gtt.gtt_remove = gen6_gmch_remove;
	}

	ret = dev_priv->gtt.gtt_probe(dev, &dev_priv->gtt.total,
				     &dev_priv->gtt.stolen_size,
				     &gtt->mappable_base,
				     &gtt->mappable_end);
	if (ret)
		return ret;

	gtt_size = (dev_priv->gtt.total >> PAGE_SHIFT) * sizeof(gen6_gtt_pte_t);

	/* GMADR is the PCI mmio aperture into the global GTT. */
	DRM_INFO("Memory usable by graphics device = %zdM\n",
		 dev_priv->gtt.total >> 20);
	DRM_DEBUG_DRIVER("GMADR size = %ldM\n",
			 dev_priv->gtt.mappable_end >> 20);
	DRM_DEBUG_DRIVER("GTT stolen size = %zdM\n",
			 dev_priv->gtt.stolen_size >> 20);

	return 0;
}