drivers/gpu/drm/i915/i915_gem_tiling.c - kernel/msm-4.19 - Gitiles

 /*
  * Copyright © 2008 Intel Corporation
  *
  * 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.
  *
  * Authors:
  *    Eric Anholt <eric@anholt.net>
  *
  */

 #include <linux/string.h>
 #include <linux/bitops.h>
 #include <drm/drmP.h>
 #include <drm/i915_drm.h>
 #include "i915_drv.h"

 /** @file i915_gem_tiling.c
  *
  * Support for managing tiling state of buffer objects.
  *
  * The idea behind tiling is to increase cache hit rates by rearranging
  * pixel data so that a group of pixel accesses are in the same cacheline.
  * Performance improvement from doing this on the back/depth buffer are on
  * the order of 30%.
  *
  * Intel architectures make this somewhat more complicated, though, by
  * adjustments made to addressing of data when the memory is in interleaved
  * mode (matched pairs of DIMMS) to improve memory bandwidth.
  * For interleaved memory, the CPU sends every sequential 64 bytes
  * to an alternate memory channel so it can get the bandwidth from both.
  *
  * The GPU also rearranges its accesses for increased bandwidth to interleaved
  * memory, and it matches what the CPU does for non-tiled.  However, when tiled
  * it does it a little differently, since one walks addresses not just in the
  * X direction but also Y.  So, along with alternating channels when bit
  * 6 of the address flips, it also alternates when other bits flip --  Bits 9
  * (every 512 bytes, an X tile scanline) and 10 (every two X tile scanlines)
  * are common to both the 915 and 965-class hardware.
  *
  * The CPU also sometimes XORs in higher bits as well, to improve
  * bandwidth doing strided access like we do so frequently in graphics.  This
  * is called "Channel XOR Randomization" in the MCH documentation.  The result
  * is that the CPU is XORing in either bit 11 or bit 17 to bit 6 of its address
  * decode.
  *
  * All of this bit 6 XORing has an effect on our memory management,
  * as we need to make sure that the 3d driver can correctly address object
  * contents.
  *
  * If we don't have interleaved memory, all tiling is safe and no swizzling is
  * required.
  *
  * When bit 17 is XORed in, we simply refuse to tile at all.  Bit
  * 17 is not just a page offset, so as we page an objet out and back in,
  * individual pages in it will have different bit 17 addresses, resulting in
  * each 64 bytes being swapped with its neighbor!
  *
  * Otherwise, if interleaved, we have to tell the 3d driver what the address
  * swizzling it needs to do is, since it's writing with the CPU to the pages
  * (bit 6 and potentially bit 11 XORed in), and the GPU is reading from the
  * pages (bit 6, 9, and 10 XORed in), resulting in a cumulative bit swizzling
  * required by the CPU of XORing in bit 6, 9, 10, and potentially 11, in order
  * to match what the GPU expects.
  */

 /**
  * Detects bit 6 swizzling of address lookup between IGD access and CPU
  * access through main memory.
  */
 void
 i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
 	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;

 	if (IS_VALLEYVIEW(dev)) {
 		swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 		swizzle_y = I915_BIT_6_SWIZZLE_NONE;
 	} else if (INTEL_INFO(dev)->gen >= 6) {
 		uint32_t dimm_c0, dimm_c1;
 		dimm_c0 = I915_READ(MAD_DIMM_C0);
 		dimm_c1 = I915_READ(MAD_DIMM_C1);
 		dimm_c0 &= MAD_DIMM_A_SIZE_MASK | MAD_DIMM_B_SIZE_MASK;
 		dimm_c1 &= MAD_DIMM_A_SIZE_MASK | MAD_DIMM_B_SIZE_MASK;
 		/* Enable swizzling when the channels are populated with
 		 * identically sized dimms. We don't need to check the 3rd
 		 * channel because no cpu with gpu attached ships in that
 		 * configuration. Also, swizzling only makes sense for 2
 		 * channels anyway. */
 		if (dimm_c0 == dimm_c1) {
 			swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 			swizzle_y = I915_BIT_6_SWIZZLE_9;
 		} else {
 			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
 		}
 	} else if (IS_GEN5(dev)) {
 		/* On Ironlake whatever DRAM config, GPU always do
 		 * same swizzling setup.
 		 */
 		swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 		swizzle_y = I915_BIT_6_SWIZZLE_9;
 	} else if (IS_GEN2(dev)) {
 		/* As far as we know, the 865 doesn't have these bit 6
 		 * swizzling issues.
 		 */
 		swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 		swizzle_y = I915_BIT_6_SWIZZLE_NONE;
 	} else if (IS_MOBILE(dev) || (IS_GEN3(dev) && !IS_G33(dev))) {
 		uint32_t dcc;

 		/* On 9xx chipsets, channel interleave by the CPU is
 		 * determined by DCC.  For single-channel, neither the CPU
 		 * nor the GPU do swizzling.  For dual channel interleaved,
 		 * the GPU's interleave is bit 9 and 10 for X tiled, and bit
 		 * 9 for Y tiled.  The CPU's interleave is independent, and
 		 * can be based on either bit 11 (haven't seen this yet) or
 		 * bit 17 (common).
 		 */
 		dcc = I915_READ(DCC);
 		switch (dcc & DCC_ADDRESSING_MODE_MASK) {
 		case DCC_ADDRESSING_MODE_SINGLE_CHANNEL:
 		case DCC_ADDRESSING_MODE_DUAL_CHANNEL_ASYMMETRIC:
 			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
 			break;
 		case DCC_ADDRESSING_MODE_DUAL_CHANNEL_INTERLEAVED:
 			if (dcc & DCC_CHANNEL_XOR_DISABLE) {
 				/* This is the base swizzling by the GPU for
 				 * tiled buffers.
 				 */
 				swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 				swizzle_y = I915_BIT_6_SWIZZLE_9;
 			} else if ((dcc & DCC_CHANNEL_XOR_BIT_17) == 0) {
 				/* Bit 11 swizzling by the CPU in addition. */
 				swizzle_x = I915_BIT_6_SWIZZLE_9_10_11;
 				swizzle_y = I915_BIT_6_SWIZZLE_9_11;
 			} else {
 				/* Bit 17 swizzling by the CPU in addition. */
 				swizzle_x = I915_BIT_6_SWIZZLE_9_10_17;
 				swizzle_y = I915_BIT_6_SWIZZLE_9_17;
 			}
 			break;
 		}
 		if (dcc == 0xffffffff) {
 			DRM_ERROR("Couldn't read from MCHBAR.  "
 				  "Disabling tiling.\n");
 			swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
 			swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
 		}
 	} else {
 		/* The 965, G33, and newer, have a very flexible memory
 		 * configuration.  It will enable dual-channel mode
 		 * (interleaving) on as much memory as it can, and the GPU
 		 * will additionally sometimes enable different bit 6
 		 * swizzling for tiled objects from the CPU.
 		 *
 		 * Here's what I found on the G965:
 		 *    slot fill         memory size  swizzling
 		 * 0A   0B   1A   1B    1-ch   2-ch
 		 * 512  0    0    0     512    0     O
 		 * 512  0    512  0     16     1008  X
 		 * 512  0    0    512   16     1008  X
 		 * 0    512  0    512   16     1008  X
 		 * 1024 1024 1024 0     2048   1024  O
 		 *
 		 * We could probably detect this based on either the DRB
 		 * matching, which was the case for the swizzling required in
 		 * the table above, or from the 1-ch value being less than
 		 * the minimum size of a rank.
 		 */
 		if (I915_READ16(C0DRB3) != I915_READ16(C1DRB3)) {
 			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
 		} else {
 			swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 			swizzle_y = I915_BIT_6_SWIZZLE_9;
 		}
 	}

 	dev_priv->mm.bit_6_swizzle_x = swizzle_x;
 	dev_priv->mm.bit_6_swizzle_y = swizzle_y;
 }

 /* Check pitch constriants for all chips & tiling formats */
 static bool
 i915_tiling_ok(struct drm_device *dev, int stride, int size, int tiling_mode)
 {
 	int tile_width;

 	/* Linear is always fine */
 	if (tiling_mode == I915_TILING_NONE)
 		return true;

 	if (IS_GEN2(dev) ||
 	    (tiling_mode == I915_TILING_Y && HAS_128_BYTE_Y_TILING(dev)))
 		tile_width = 128;
 	else
 		tile_width = 512;

 	/* check maximum stride & object size */
 	if (INTEL_INFO(dev)->gen >= 4) {
 		/* i965 stores the end address of the gtt mapping in the fence
 		 * reg, so dont bother to check the size */
 		if (stride / 128 > I965_FENCE_MAX_PITCH_VAL)
 			return false;
 	} else {
 		if (stride > 8192)
 			return false;

 		if (IS_GEN3(dev)) {
 			if (size > I830_FENCE_MAX_SIZE_VAL << 20)
 				return false;
 		} else {
 			if (size > I830_FENCE_MAX_SIZE_VAL << 19)
 				return false;
 		}
 	}

 	/* 965+ just needs multiples of tile width */
 	if (INTEL_INFO(dev)->gen >= 4) {
 		if (stride & (tile_width - 1))
 			return false;
 		return true;
 	}

 	/* Pre-965 needs power of two tile widths */
 	if (stride < tile_width)
 		return false;

 	if (stride & (stride - 1))
 		return false;

 	return true;
 }

 /* Is the current GTT allocation valid for the change in tiling? */
 static bool
 i915_gem_object_fence_ok(struct drm_i915_gem_object *obj, int tiling_mode)
 {
 	u32 size;

 	if (tiling_mode == I915_TILING_NONE)
 		return true;

 	if (INTEL_INFO(obj->base.dev)->gen >= 4)
 		return true;

 	if (INTEL_INFO(obj->base.dev)->gen == 3) {
 		if (obj->gtt_offset & ~I915_FENCE_START_MASK)
 			return false;
 	} else {
 		if (obj->gtt_offset & ~I830_FENCE_START_MASK)
 			return false;
 	}

 	size = i915_gem_get_gtt_size(obj->base.dev, obj->base.size, tiling_mode);
 	if (obj->gtt_space->size != size)
 		return false;

 	if (obj->gtt_offset & (size - 1))
 		return false;

 	return true;
 }

 /**
  * Sets the tiling mode of an object, returning the required swizzling of
  * bit 6 of addresses in the object.
  */
 int
 i915_gem_set_tiling(struct drm_device *dev, void *data,
 		   struct drm_file *file)
 {
 	struct drm_i915_gem_set_tiling *args = data;
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj;
 	int ret = 0;

 	obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
 	if (&obj->base == NULL)
 		return -ENOENT;

 	if (!i915_tiling_ok(dev,
 			    args->stride, obj->base.size, args->tiling_mode)) {
 		drm_gem_object_unreference_unlocked(&obj->base);
 		return -EINVAL;
 	}

 	if (obj->pin_count) {
 		drm_gem_object_unreference_unlocked(&obj->base);
 		return -EBUSY;
 	}

 	if (args->tiling_mode == I915_TILING_NONE) {
 		args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
 		args->stride = 0;
 	} else {
 		if (args->tiling_mode == I915_TILING_X)
 			args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
 		else
 			args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;

 		/* Hide bit 17 swizzling from the user.  This prevents old Mesa
 		 * from aborting the application on sw fallbacks to bit 17,
 		 * and we use the pread/pwrite bit17 paths to swizzle for it.
 		 * If there was a user that was relying on the swizzle
 		 * information for drm_intel_bo_map()ed reads/writes this would
 		 * break it, but we don't have any of those.
 		 */
 		if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_17)
 			args->swizzle_mode = I915_BIT_6_SWIZZLE_9;
 		if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_10_17)
 			args->swizzle_mode = I915_BIT_6_SWIZZLE_9_10;

 		/* If we can't handle the swizzling, make it untiled. */
 		if (args->swizzle_mode == I915_BIT_6_SWIZZLE_UNKNOWN) {
 			args->tiling_mode = I915_TILING_NONE;
 			args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
 			args->stride = 0;
 		}
 	}

 	mutex_lock(&dev->struct_mutex);
 	if (args->tiling_mode != obj->tiling_mode ||
 	    args->stride != obj->stride) {
 		/* We need to rebind the object if its current allocation
 		 * no longer meets the alignment restrictions for its new
 		 * tiling mode. Otherwise we can just leave it alone, but
 		 * need to ensure that any fence register is updated before
 		 * the next fenced (either through the GTT or by the BLT unit
 		 * on older GPUs) access.
 		 *
 		 * After updating the tiling parameters, we then flag whether
 		 * we need to update an associated fence register. Note this
 		 * has to also include the unfenced register the GPU uses
 		 * whilst executing a fenced command for an untiled object.
 		 */

 		obj->map_and_fenceable =
 			obj->gtt_space == NULL ||
 			(obj->gtt_offset + obj->base.size <= dev_priv->mm.gtt_mappable_end &&
 			 i915_gem_object_fence_ok(obj, args->tiling_mode));

 		/* Rebind if we need a change of alignment */
 		if (!obj->map_and_fenceable) {
 			u32 unfenced_alignment =
 				i915_gem_get_gtt_alignment(dev, obj->base.size,
 							    args->tiling_mode,
 							    false);
 			if (obj->gtt_offset & (unfenced_alignment - 1))
 				ret = i915_gem_object_unbind(obj);
 		}

 		if (ret == 0) {
 			obj->fence_dirty =
 				obj->fenced_gpu_access ||
 				obj->fence_reg != I915_FENCE_REG_NONE;

 			obj->tiling_mode = args->tiling_mode;
 			obj->stride = args->stride;

 			/* Force the fence to be reacquired for GTT access */
 			i915_gem_release_mmap(obj);
 		}
 	}
 	/* we have to maintain this existing ABI... */
 	args->stride = obj->stride;
 	args->tiling_mode = obj->tiling_mode;

 	/* Try to preallocate memory required to save swizzling on put-pages */
 	if (i915_gem_object_needs_bit17_swizzle(obj)) {
 		if (obj->bit_17 == NULL) {
 			obj->bit_17 = kmalloc(BITS_TO_LONGS(obj->base.size >> PAGE_SHIFT) *
 					      sizeof(long), GFP_KERNEL);
 		}
 	} else {
 		kfree(obj->bit_17);
 		obj->bit_17 = NULL;
 	}

 	drm_gem_object_unreference(&obj->base);
 	mutex_unlock(&dev->struct_mutex);

 	return ret;
 }

 /**
  * Returns the current tiling mode and required bit 6 swizzling for the object.
  */
 int
 i915_gem_get_tiling(struct drm_device *dev, void *data,
 		   struct drm_file *file)
 {
 	struct drm_i915_gem_get_tiling *args = data;
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj;

 	obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
 	if (&obj->base == NULL)
 		return -ENOENT;

 	mutex_lock(&dev->struct_mutex);

 	args->tiling_mode = obj->tiling_mode;
 	switch (obj->tiling_mode) {
 	case I915_TILING_X:
 		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
 		break;
 	case I915_TILING_Y:
 		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;
 		break;
 	case I915_TILING_NONE:
 		args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
 		break;
 	default:
 		DRM_ERROR("unknown tiling mode\n");
 	}

 	/* Hide bit 17 from the user -- see comment in i915_gem_set_tiling */
 	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_17)
 		args->swizzle_mode = I915_BIT_6_SWIZZLE_9;
 	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_10_17)
 		args->swizzle_mode = I915_BIT_6_SWIZZLE_9_10;

 	drm_gem_object_unreference(&obj->base);
 	mutex_unlock(&dev->struct_mutex);

 	return 0;
 }

 /**
  * Swap every 64 bytes of this page around, to account for it having a new
  * bit 17 of its physical address and therefore being interpreted differently
  * by the GPU.
  */
 static void
 i915_gem_swizzle_page(struct page *page)
 {
 	char temp[64];
 	char *vaddr;
 	int i;

 	vaddr = kmap(page);

 	for (i = 0; i < PAGE_SIZE; i += 128) {
 		memcpy(temp, &vaddr[i], 64);
 		memcpy(&vaddr[i], &vaddr[i + 64], 64);
 		memcpy(&vaddr[i + 64], temp, 64);
 	}

 	kunmap(page);
 }

 void
 i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
 	struct scatterlist *sg;
 	int page_count = obj->base.size >> PAGE_SHIFT;
 	int i;

 	if (obj->bit_17 == NULL)
 		return;

 	for_each_sg(obj->pages->sgl, sg, page_count, i) {
 		struct page *page = sg_page(sg);
 		char new_bit_17 = page_to_phys(page) >> 17;
 		if ((new_bit_17 & 0x1) !=
 		    (test_bit(i, obj->bit_17) != 0)) {
 			i915_gem_swizzle_page(page);
 			set_page_dirty(page);
 		}
 	}
 }

 void
 i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
 	struct scatterlist *sg;
 	int page_count = obj->base.size >> PAGE_SHIFT;
 	int i;

 	if (obj->bit_17 == NULL) {
 		obj->bit_17 = kmalloc(BITS_TO_LONGS(page_count) *
 					   sizeof(long), GFP_KERNEL);
 		if (obj->bit_17 == NULL) {
 			DRM_ERROR("Failed to allocate memory for bit 17 "
 				  "record\n");
 			return;
 		}
 	}

 	for_each_sg(obj->pages->sgl, sg, page_count, i) {
 		struct page *page = sg_page(sg);
 		if (page_to_phys(page) & (1 << 17))
 			__set_bit(i, obj->bit_17);
 		else
 			__clear_bit(i, obj->bit_17);
 	}
 }
	/*
	* Copyright © 2008 Intel Corporation
	*
	* 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.
	*
	* Authors:
	* Eric Anholt <eric@anholt.net>
	*
	*/

	#include <linux/string.h>
	#include <linux/bitops.h>
	#include <drm/drmP.h>
	#include <drm/i915_drm.h>
	#include "i915_drv.h"

	/** @file i915_gem_tiling.c
	*
	* Support for managing tiling state of buffer objects.
	*
	* The idea behind tiling is to increase cache hit rates by rearranging
	* pixel data so that a group of pixel accesses are in the same cacheline.
	* Performance improvement from doing this on the back/depth buffer are on
	* the order of 30%.
	*
	* Intel architectures make this somewhat more complicated, though, by
	* adjustments made to addressing of data when the memory is in interleaved
	* mode (matched pairs of DIMMS) to improve memory bandwidth.
	* For interleaved memory, the CPU sends every sequential 64 bytes
	* to an alternate memory channel so it can get the bandwidth from both.
	*
	* The GPU also rearranges its accesses for increased bandwidth to interleaved
	* memory, and it matches what the CPU does for non-tiled. However, when tiled
	* it does it a little differently, since one walks addresses not just in the
	* X direction but also Y. So, along with alternating channels when bit
	* 6 of the address flips, it also alternates when other bits flip -- Bits 9
	* (every 512 bytes, an X tile scanline) and 10 (every two X tile scanlines)
	* are common to both the 915 and 965-class hardware.
	*
	* The CPU also sometimes XORs in higher bits as well, to improve
	* bandwidth doing strided access like we do so frequently in graphics. This
	* is called "Channel XOR Randomization" in the MCH documentation. The result
	* is that the CPU is XORing in either bit 11 or bit 17 to bit 6 of its address
	* decode.
	*
	* All of this bit 6 XORing has an effect on our memory management,
	* as we need to make sure that the 3d driver can correctly address object
	* contents.
	*
	* If we don't have interleaved memory, all tiling is safe and no swizzling is
	* required.
	*
	* When bit 17 is XORed in, we simply refuse to tile at all. Bit
	* 17 is not just a page offset, so as we page an objet out and back in,
	* individual pages in it will have different bit 17 addresses, resulting in
	* each 64 bytes being swapped with its neighbor!
	*
	* Otherwise, if interleaved, we have to tell the 3d driver what the address
	* swizzling it needs to do is, since it's writing with the CPU to the pages
	* (bit 6 and potentially bit 11 XORed in), and the GPU is reading from the
	* pages (bit 6, 9, and 10 XORed in), resulting in a cumulative bit swizzling
	* required by the CPU of XORing in bit 6, 9, 10, and potentially 11, in order
	* to match what the GPU expects.
	*/

	/**
	* Detects bit 6 swizzling of address lookup between IGD access and CPU
	* access through main memory.
	*/
	void
	i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
	{
	drm_i915_private_t *dev_priv = dev->dev_private;
	uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;

	if (IS_VALLEYVIEW(dev)) {
	swizzle_x = I915_BIT_6_SWIZZLE_NONE;
	swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	} else if (INTEL_INFO(dev)->gen >= 6) {
	uint32_t dimm_c0, dimm_c1;
	dimm_c0 = I915_READ(MAD_DIMM_C0);
	dimm_c1 = I915_READ(MAD_DIMM_C1);
	dimm_c0 &= MAD_DIMM_A_SIZE_MASK \| MAD_DIMM_B_SIZE_MASK;
	dimm_c1 &= MAD_DIMM_A_SIZE_MASK \| MAD_DIMM_B_SIZE_MASK;
	/* Enable swizzling when the channels are populated with
	* identically sized dimms. We don't need to check the 3rd
	* channel because no cpu with gpu attached ships in that
	* configuration. Also, swizzling only makes sense for 2
	* channels anyway. */
	if (dimm_c0 == dimm_c1) {
	swizzle_x = I915_BIT_6_SWIZZLE_9_10;
	swizzle_y = I915_BIT_6_SWIZZLE_9;
	} else {
	swizzle_x = I915_BIT_6_SWIZZLE_NONE;
	swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	}
	} else if (IS_GEN5(dev)) {
	/* On Ironlake whatever DRAM config, GPU always do
	* same swizzling setup.
	*/
	swizzle_x = I915_BIT_6_SWIZZLE_9_10;
	swizzle_y = I915_BIT_6_SWIZZLE_9;
	} else if (IS_GEN2(dev)) {
	/* As far as we know, the 865 doesn't have these bit 6
	* swizzling issues.
	*/
	swizzle_x = I915_BIT_6_SWIZZLE_NONE;
	swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	} else if (IS_MOBILE(dev) \|\| (IS_GEN3(dev) && !IS_G33(dev))) {
	uint32_t dcc;

	/* On 9xx chipsets, channel interleave by the CPU is
	* determined by DCC. For single-channel, neither the CPU
	* nor the GPU do swizzling. For dual channel interleaved,
	* the GPU's interleave is bit 9 and 10 for X tiled, and bit
	* 9 for Y tiled. The CPU's interleave is independent, and
	* can be based on either bit 11 (haven't seen this yet) or
	* bit 17 (common).
	*/
	dcc = I915_READ(DCC);
	switch (dcc & DCC_ADDRESSING_MODE_MASK) {
	case DCC_ADDRESSING_MODE_SINGLE_CHANNEL:
	case DCC_ADDRESSING_MODE_DUAL_CHANNEL_ASYMMETRIC:
	swizzle_x = I915_BIT_6_SWIZZLE_NONE;
	swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	break;
	case DCC_ADDRESSING_MODE_DUAL_CHANNEL_INTERLEAVED:
	if (dcc & DCC_CHANNEL_XOR_DISABLE) {
	/* This is the base swizzling by the GPU for
	* tiled buffers.
	*/
	swizzle_x = I915_BIT_6_SWIZZLE_9_10;
	swizzle_y = I915_BIT_6_SWIZZLE_9;
	} else if ((dcc & DCC_CHANNEL_XOR_BIT_17) == 0) {
	/* Bit 11 swizzling by the CPU in addition. */
	swizzle_x = I915_BIT_6_SWIZZLE_9_10_11;
	swizzle_y = I915_BIT_6_SWIZZLE_9_11;
	} else {
	/* Bit 17 swizzling by the CPU in addition. */
	swizzle_x = I915_BIT_6_SWIZZLE_9_10_17;
	swizzle_y = I915_BIT_6_SWIZZLE_9_17;
	}
	break;
	}
	if (dcc == 0xffffffff) {
	DRM_ERROR("Couldn't read from MCHBAR. "
	"Disabling tiling.\n");
	swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
	swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
	}
	} else {
	/* The 965, G33, and newer, have a very flexible memory
	* configuration. It will enable dual-channel mode
	* (interleaving) on as much memory as it can, and the GPU
	* will additionally sometimes enable different bit 6
	* swizzling for tiled objects from the CPU.
	*
	* Here's what I found on the G965:
	* slot fill memory size swizzling
	* 0A 0B 1A 1B 1-ch 2-ch
	* 512 0 0 0 512 0 O
	* 512 0 512 0 16 1008 X
	* 512 0 0 512 16 1008 X
	* 0 512 0 512 16 1008 X
	* 1024 1024 1024 0 2048 1024 O
	*
	* We could probably detect this based on either the DRB
	* matching, which was the case for the swizzling required in
	* the table above, or from the 1-ch value being less than
	* the minimum size of a rank.
	*/
	if (I915_READ16(C0DRB3) != I915_READ16(C1DRB3)) {
	swizzle_x = I915_BIT_6_SWIZZLE_NONE;
	swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	} else {
	swizzle_x = I915_BIT_6_SWIZZLE_9_10;
	swizzle_y = I915_BIT_6_SWIZZLE_9;
	}
	}

	dev_priv->mm.bit_6_swizzle_x = swizzle_x;
	dev_priv->mm.bit_6_swizzle_y = swizzle_y;
	}

	/* Check pitch constriants for all chips & tiling formats */
	static bool
	i915_tiling_ok(struct drm_device *dev, int stride, int size, int tiling_mode)
	{
	int tile_width;

	/* Linear is always fine */
	if (tiling_mode == I915_TILING_NONE)
	return true;

	if (IS_GEN2(dev) \|\|
	(tiling_mode == I915_TILING_Y && HAS_128_BYTE_Y_TILING(dev)))
	tile_width = 128;
	else
	tile_width = 512;

	/* check maximum stride & object size */
	if (INTEL_INFO(dev)->gen >= 4) {
	/* i965 stores the end address of the gtt mapping in the fence
	* reg, so dont bother to check the size */
	if (stride / 128 > I965_FENCE_MAX_PITCH_VAL)
	return false;
	} else {
	if (stride > 8192)
	return false;

	if (IS_GEN3(dev)) {
	if (size > I830_FENCE_MAX_SIZE_VAL << 20)
	return false;
	} else {
	if (size > I830_FENCE_MAX_SIZE_VAL << 19)
	return false;
	}
	}

	/* 965+ just needs multiples of tile width */
	if (INTEL_INFO(dev)->gen >= 4) {
	if (stride & (tile_width - 1))
	return false;
	return true;
	}

	/* Pre-965 needs power of two tile widths */
	if (stride < tile_width)
	return false;

	if (stride & (stride - 1))
	return false;

	return true;
	}

	/* Is the current GTT allocation valid for the change in tiling? */
	static bool
	i915_gem_object_fence_ok(struct drm_i915_gem_object *obj, int tiling_mode)
	{
	u32 size;

	if (tiling_mode == I915_TILING_NONE)
	return true;

	if (INTEL_INFO(obj->base.dev)->gen >= 4)
	return true;

	if (INTEL_INFO(obj->base.dev)->gen == 3) {
	if (obj->gtt_offset & ~I915_FENCE_START_MASK)
	return false;
	} else {
	if (obj->gtt_offset & ~I830_FENCE_START_MASK)
	return false;
	}

	size = i915_gem_get_gtt_size(obj->base.dev, obj->base.size, tiling_mode);
	if (obj->gtt_space->size != size)
	return false;

	if (obj->gtt_offset & (size - 1))
	return false;

	return true;
	}

	/**
	* Sets the tiling mode of an object, returning the required swizzling of
	* bit 6 of addresses in the object.
	*/
	int
	i915_gem_set_tiling(struct drm_device dev, void data,
	struct drm_file *file)
	{
	struct drm_i915_gem_set_tiling *args = data;
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct drm_i915_gem_object *obj;
	int ret = 0;

	obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
	if (&obj->base == NULL)
	return -ENOENT;

	if (!i915_tiling_ok(dev,
	args->stride, obj->base.size, args->tiling_mode)) {
	drm_gem_object_unreference_unlocked(&obj->base);
	return -EINVAL;
	}

	if (obj->pin_count) {
	drm_gem_object_unreference_unlocked(&obj->base);
	return -EBUSY;
	}

	if (args->tiling_mode == I915_TILING_NONE) {
	args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
	args->stride = 0;
	} else {
	if (args->tiling_mode == I915_TILING_X)
	args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
	else
	args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;

	/* Hide bit 17 swizzling from the user. This prevents old Mesa
	* from aborting the application on sw fallbacks to bit 17,
	* and we use the pread/pwrite bit17 paths to swizzle for it.
	* If there was a user that was relying on the swizzle
	* information for drm_intel_bo_map()ed reads/writes this would
	* break it, but we don't have any of those.
	*/
	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_17)
	args->swizzle_mode = I915_BIT_6_SWIZZLE_9;
	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_10_17)
	args->swizzle_mode = I915_BIT_6_SWIZZLE_9_10;

	/* If we can't handle the swizzling, make it untiled. */
	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_UNKNOWN) {
	args->tiling_mode = I915_TILING_NONE;
	args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
	args->stride = 0;
	}
	}

	mutex_lock(&dev->struct_mutex);
	if (args->tiling_mode != obj->tiling_mode \|\|
	args->stride != obj->stride) {
	/* We need to rebind the object if its current allocation
	* no longer meets the alignment restrictions for its new
	* tiling mode. Otherwise we can just leave it alone, but
	* need to ensure that any fence register is updated before
	* the next fenced (either through the GTT or by the BLT unit
	* on older GPUs) access.
	*
	* After updating the tiling parameters, we then flag whether
	* we need to update an associated fence register. Note this
	* has to also include the unfenced register the GPU uses
	* whilst executing a fenced command for an untiled object.
	*/

	obj->map_and_fenceable =
	obj->gtt_space == NULL \|\|
	(obj->gtt_offset + obj->base.size <= dev_priv->mm.gtt_mappable_end &&
	i915_gem_object_fence_ok(obj, args->tiling_mode));

	/* Rebind if we need a change of alignment */
	if (!obj->map_and_fenceable) {
	u32 unfenced_alignment =
	i915_gem_get_gtt_alignment(dev, obj->base.size,
	args->tiling_mode,
	false);
	if (obj->gtt_offset & (unfenced_alignment - 1))
	ret = i915_gem_object_unbind(obj);
	}

	if (ret == 0) {
	obj->fence_dirty =
	obj->fenced_gpu_access \|\|
	obj->fence_reg != I915_FENCE_REG_NONE;

	obj->tiling_mode = args->tiling_mode;
	obj->stride = args->stride;

	/* Force the fence to be reacquired for GTT access */
	i915_gem_release_mmap(obj);
	}
	}
	/* we have to maintain this existing ABI... */
	args->stride = obj->stride;
	args->tiling_mode = obj->tiling_mode;

	/* Try to preallocate memory required to save swizzling on put-pages */
	if (i915_gem_object_needs_bit17_swizzle(obj)) {
	if (obj->bit_17 == NULL) {
	obj->bit_17 = kmalloc(BITS_TO_LONGS(obj->base.size >> PAGE_SHIFT) *
	sizeof(long), GFP_KERNEL);
	}
	} else {
	kfree(obj->bit_17);
	obj->bit_17 = NULL;
	}

	drm_gem_object_unreference(&obj->base);
	mutex_unlock(&dev->struct_mutex);

	return ret;
	}

	/**
	* Returns the current tiling mode and required bit 6 swizzling for the object.
	*/
	int
	i915_gem_get_tiling(struct drm_device dev, void data,
	struct drm_file *file)
	{
	struct drm_i915_gem_get_tiling *args = data;
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct drm_i915_gem_object *obj;

	obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
	if (&obj->base == NULL)
	return -ENOENT;

	mutex_lock(&dev->struct_mutex);

	args->tiling_mode = obj->tiling_mode;
	switch (obj->tiling_mode) {
	case I915_TILING_X:
	args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
	break;
	case I915_TILING_Y:
	args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;
	break;
	case I915_TILING_NONE:
	args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
	break;
	default:
	DRM_ERROR("unknown tiling mode\n");
	}

	/* Hide bit 17 from the user -- see comment in i915_gem_set_tiling */
	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_17)
	args->swizzle_mode = I915_BIT_6_SWIZZLE_9;
	if (args->swizzle_mode == I915_BIT_6_SWIZZLE_9_10_17)
	args->swizzle_mode = I915_BIT_6_SWIZZLE_9_10;

	drm_gem_object_unreference(&obj->base);
	mutex_unlock(&dev->struct_mutex);

	return 0;
	}

	/**
	* Swap every 64 bytes of this page around, to account for it having a new
	* bit 17 of its physical address and therefore being interpreted differently
	* by the GPU.
	*/
	static void
	i915_gem_swizzle_page(struct page *page)
	{
	char temp[64];
	char *vaddr;
	int i;

	vaddr = kmap(page);

	for (i = 0; i < PAGE_SIZE; i += 128) {
	memcpy(temp, &vaddr[i], 64);
	memcpy(&vaddr[i], &vaddr[i + 64], 64);
	memcpy(&vaddr[i + 64], temp, 64);
	}

	kunmap(page);
	}

	void
	i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj)
	{
	struct scatterlist *sg;
	int page_count = obj->base.size >> PAGE_SHIFT;
	int i;

	if (obj->bit_17 == NULL)
	return;

	for_each_sg(obj->pages->sgl, sg, page_count, i) {
	struct page *page = sg_page(sg);
	char new_bit_17 = page_to_phys(page) >> 17;
	if ((new_bit_17 & 0x1) !=
	(test_bit(i, obj->bit_17) != 0)) {
	i915_gem_swizzle_page(page);
	set_page_dirty(page);
	}
	}
	}

	void
	i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj)
	{
	struct scatterlist *sg;
	int page_count = obj->base.size >> PAGE_SHIFT;
	int i;

	if (obj->bit_17 == NULL) {
	obj->bit_17 = kmalloc(BITS_TO_LONGS(page_count) *
	sizeof(long), GFP_KERNEL);
	if (obj->bit_17 == NULL) {
	DRM_ERROR("Failed to allocate memory for bit 17 "
	"record\n");
	return;
	}
	}

	for_each_sg(obj->pages->sgl, sg, page_count, i) {
	struct page *page = sg_page(sg);
	if (page_to_phys(page) & (1 << 17))
	__set_bit(i, obj->bit_17);
	else
	__clear_bit(i, obj->bit_17);
	}
	}