drivers/gpu/drm/i915/gt/intel_gtt.c - linux - Git at Google

 // SPDX-License-Identifier: MIT
 /*
  * Copyright © 2020 Intel Corporation
  */

 #include <linux/slab.h> /* fault-inject.h is not standalone! */

 #include <linux/fault-inject.h>

 #include "i915_trace.h"
 #include "intel_gt.h"
 #include "intel_gtt.h"

 struct drm_i915_gem_object *alloc_pt_dma(struct i915_address_space *vm, int sz)
 {
 	if (I915_SELFTEST_ONLY(should_fail(&vm->fault_attr, 1)))
 		i915_gem_shrink_all(vm->i915);

 	return i915_gem_object_create_internal(vm->i915, sz);
 }

 int pin_pt_dma(struct i915_address_space *vm, struct drm_i915_gem_object *obj)
 {
 	int err;

 	err = i915_gem_object_pin_pages(obj);
 	if (err)
 		return err;

 	i915_gem_object_make_unshrinkable(obj);
 	return 0;
 }

 void __i915_vm_close(struct i915_address_space *vm)
 {
 	struct i915_vma *vma, *vn;

 	if (!atomic_dec_and_mutex_lock(&vm->open, &vm->mutex))
 		return;

 	list_for_each_entry_safe(vma, vn, &vm->bound_list, vm_link) {
 		struct drm_i915_gem_object *obj = vma->obj;

 		/* Keep the obj (and hence the vma) alive as _we_ destroy it */
 		if (!kref_get_unless_zero(&obj->base.refcount))
 			continue;

 		atomic_and(~I915_VMA_PIN_MASK, &vma->flags);
 		WARN_ON(__i915_vma_unbind(vma));
 		__i915_vma_put(vma);

 		i915_gem_object_put(obj);
 	}
 	GEM_BUG_ON(!list_empty(&vm->bound_list));

 	mutex_unlock(&vm->mutex);
 }

 void i915_address_space_fini(struct i915_address_space *vm)
 {
 	drm_mm_takedown(&vm->mm);
 	mutex_destroy(&vm->mutex);
 }

 static void __i915_vm_release(struct work_struct *work)
 {
 	struct i915_address_space *vm =
 		container_of(work, struct i915_address_space, rcu.work);

 	vm->cleanup(vm);
 	i915_address_space_fini(vm);

 	kfree(vm);
 }

 void i915_vm_release(struct kref *kref)
 {
 	struct i915_address_space *vm =
 		container_of(kref, struct i915_address_space, ref);

 	GEM_BUG_ON(i915_is_ggtt(vm));
 	trace_i915_ppgtt_release(vm);

 	queue_rcu_work(vm->i915->wq, &vm->rcu);
 }

 void i915_address_space_init(struct i915_address_space *vm, int subclass)
 {
 	kref_init(&vm->ref);
 	INIT_RCU_WORK(&vm->rcu, __i915_vm_release);
 	atomic_set(&vm->open, 1);

 	/*
 	 * The vm->mutex must be reclaim safe (for use in the shrinker).
 	 * Do a dummy acquire now under fs_reclaim so that any allocation
 	 * attempt holding the lock is immediately reported by lockdep.
 	 */
 	mutex_init(&vm->mutex);
 	lockdep_set_subclass(&vm->mutex, subclass);
 	i915_gem_shrinker_taints_mutex(vm->i915, &vm->mutex);

 	GEM_BUG_ON(!vm->total);
 	drm_mm_init(&vm->mm, 0, vm->total);
 	vm->mm.head_node.color = I915_COLOR_UNEVICTABLE;

 	INIT_LIST_HEAD(&vm->bound_list);
 }

 void clear_pages(struct i915_vma *vma)
 {
 	GEM_BUG_ON(!vma->pages);

 	if (vma->pages != vma->obj->mm.pages) {
 		sg_free_table(vma->pages);
 		kfree(vma->pages);
 	}
 	vma->pages = NULL;

 	memset(&vma->page_sizes, 0, sizeof(vma->page_sizes));
 }

 dma_addr_t __px_dma(struct drm_i915_gem_object *p)
 {
 	GEM_BUG_ON(!i915_gem_object_has_pages(p));
 	return sg_dma_address(p->mm.pages->sgl);
 }

 struct page *__px_page(struct drm_i915_gem_object *p)
 {
 	GEM_BUG_ON(!i915_gem_object_has_pages(p));
 	return sg_page(p->mm.pages->sgl);
 }

 void
 fill_page_dma(struct drm_i915_gem_object *p, const u64 val, unsigned int count)
 {
 	struct page *page = __px_page(p);
 	void *vaddr;

 	vaddr = kmap(page);
 	memset64(vaddr, val, count);
 	clflush_cache_range(vaddr, PAGE_SIZE);
 	kunmap(page);
 }

 static void poison_scratch_page(struct drm_i915_gem_object *scratch)
 {
 	struct sgt_iter sgt;
 	struct page *page;
 	u8 val;

 	val = 0;
 	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
 		val = POISON_FREE;

 	for_each_sgt_page(page, sgt, scratch->mm.pages) {
 		void *vaddr;

 		vaddr = kmap(page);
 		memset(vaddr, val, PAGE_SIZE);
 		kunmap(page);
 	}
 }

 int setup_scratch_page(struct i915_address_space *vm)
 {
 	unsigned long size;

 	/*
 	 * In order to utilize 64K pages for an object with a size < 2M, we will
 	 * need to support a 64K scratch page, given that every 16th entry for a
 	 * page-table operating in 64K mode must point to a properly aligned 64K
 	 * region, including any PTEs which happen to point to scratch.
 	 *
 	 * This is only relevant for the 48b PPGTT where we support
 	 * huge-gtt-pages, see also i915_vma_insert(). However, as we share the
 	 * scratch (read-only) between all vm, we create one 64k scratch page
 	 * for all.
 	 */
 	size = I915_GTT_PAGE_SIZE_4K;
 	if (i915_vm_is_4lvl(vm) &&
 	    HAS_PAGE_SIZES(vm->i915, I915_GTT_PAGE_SIZE_64K))
 		size = I915_GTT_PAGE_SIZE_64K;

 	do {
 		struct drm_i915_gem_object *obj;

 		obj = vm->alloc_pt_dma(vm, size);
 		if (IS_ERR(obj))
 			goto skip;

 		if (pin_pt_dma(vm, obj))
 			goto skip_obj;

 		/* We need a single contiguous page for our scratch */
 		if (obj->mm.page_sizes.sg < size)
 			goto skip_obj;

 		/* And it needs to be correspondingly aligned */
 		if (__px_dma(obj) & (size - 1))
 			goto skip_obj;

 		/*
 		 * Use a non-zero scratch page for debugging.
 		 *
 		 * We want a value that should be reasonably obvious
 		 * to spot in the error state, while also causing a GPU hang
 		 * if executed. We prefer using a clear page in production, so
 		 * should it ever be accidentally used, the effect should be
 		 * fairly benign.
 		 */
 		poison_scratch_page(obj);

 		vm->scratch[0] = obj;
 		vm->scratch_order = get_order(size);
 		return 0;

 skip_obj:
 		i915_gem_object_put(obj);
 skip:
 		if (size == I915_GTT_PAGE_SIZE_4K)
 			return -ENOMEM;

 		size = I915_GTT_PAGE_SIZE_4K;
 	} while (1);
 }

 void free_scratch(struct i915_address_space *vm)
 {
 	int i;

 	for (i = 0; i <= vm->top; i++)
 		i915_gem_object_put(vm->scratch[i]);
 }

 void gtt_write_workarounds(struct intel_gt *gt)
 {
 	struct drm_i915_private *i915 = gt->i915;
 	struct intel_uncore *uncore = gt->uncore;

 	/*
 	 * This function is for gtt related workarounds. This function is
 	 * called on driver load and after a GPU reset, so you can place
 	 * workarounds here even if they get overwritten by GPU reset.
 	 */
 	/* WaIncreaseDefaultTLBEntries:chv,bdw,skl,bxt,kbl,glk,cfl,cnl,icl */
 	if (IS_BROADWELL(i915))
 		intel_uncore_write(uncore,
 				   GEN8_L3_LRA_1_GPGPU,
 				   GEN8_L3_LRA_1_GPGPU_DEFAULT_VALUE_BDW);
 	else if (IS_CHERRYVIEW(i915))
 		intel_uncore_write(uncore,
 				   GEN8_L3_LRA_1_GPGPU,
 				   GEN8_L3_LRA_1_GPGPU_DEFAULT_VALUE_CHV);
 	else if (IS_GEN9_LP(i915))
 		intel_uncore_write(uncore,
 				   GEN8_L3_LRA_1_GPGPU,
 				   GEN9_L3_LRA_1_GPGPU_DEFAULT_VALUE_BXT);
 	else if (INTEL_GEN(i915) >= 9 && INTEL_GEN(i915) <= 11)
 		intel_uncore_write(uncore,
 				   GEN8_L3_LRA_1_GPGPU,
 				   GEN9_L3_LRA_1_GPGPU_DEFAULT_VALUE_SKL);

 	/*
 	 * To support 64K PTEs we need to first enable the use of the
 	 * Intermediate-Page-Size(IPS) bit of the PDE field via some magical
 	 * mmio, otherwise the page-walker will simply ignore the IPS bit. This
 	 * shouldn't be needed after GEN10.
 	 *
 	 * 64K pages were first introduced from BDW+, although technically they
 	 * only *work* from gen9+. For pre-BDW we instead have the option for
 	 * 32K pages, but we don't currently have any support for it in our
 	 * driver.
 	 */
 	if (HAS_PAGE_SIZES(i915, I915_GTT_PAGE_SIZE_64K) &&
 	    INTEL_GEN(i915) <= 10)
 		intel_uncore_rmw(uncore,
 				 GEN8_GAMW_ECO_DEV_RW_IA,
 				 0,
 				 GAMW_ECO_ENABLE_64K_IPS_FIELD);

 	if (IS_GEN_RANGE(i915, 8, 11)) {
 		bool can_use_gtt_cache = true;

 		/*
 		 * According to the BSpec if we use 2M/1G pages then we also
 		 * need to disable the GTT cache. At least on BDW we can see
 		 * visual corruption when using 2M pages, and not disabling the
 		 * GTT cache.
 		 */
 		if (HAS_PAGE_SIZES(i915, I915_GTT_PAGE_SIZE_2M))
 			can_use_gtt_cache = false;

 		/* WaGttCachingOffByDefault */
 		intel_uncore_write(uncore,
 				   HSW_GTT_CACHE_EN,
 				   can_use_gtt_cache ? GTT_CACHE_EN_ALL : 0);
 		drm_WARN_ON_ONCE(&i915->drm, can_use_gtt_cache &&
 				 intel_uncore_read(uncore,
 						   HSW_GTT_CACHE_EN) == 0);
 	}
 }

 static void tgl_setup_private_ppat(struct intel_uncore *uncore)
 {
 	/* TGL doesn't support LLC or AGE settings */
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(0), GEN8_PPAT_WB);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(1), GEN8_PPAT_WC);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(2), GEN8_PPAT_WT);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(3), GEN8_PPAT_UC);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(4), GEN8_PPAT_WB);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(5), GEN8_PPAT_WB);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(6), GEN8_PPAT_WB);
 	intel_uncore_write(uncore, GEN12_PAT_INDEX(7), GEN8_PPAT_WB);
 }

 static void cnl_setup_private_ppat(struct intel_uncore *uncore)
 {
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(0),
 			   GEN8_PPAT_WB | GEN8_PPAT_LLC);
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(1),
 			   GEN8_PPAT_WC | GEN8_PPAT_LLCELLC);
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(2),
 			   GEN8_PPAT_WB | GEN8_PPAT_ELLC_OVERRIDE);
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(3),
 			   GEN8_PPAT_UC);
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(4),
 			   GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0));
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(5),
 			   GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1));
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(6),
 			   GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2));
 	intel_uncore_write(uncore,
 			   GEN10_PAT_INDEX(7),
 			   GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));
 }

 /*
  * The GGTT and PPGTT need a private PPAT setup in order to handle cacheability
  * bits. When using advanced contexts each context stores its own PAT, but
  * writing this data shouldn't be harmful even in those cases.
  */
 static void bdw_setup_private_ppat(struct intel_uncore *uncore)
 {
 	struct drm_i915_private *i915 = uncore->i915;
 	u64 pat;

 	pat = GEN8_PPAT(0, GEN8_PPAT_WB | GEN8_PPAT_LLC) |	/* for normal objects, no eLLC */
 	      GEN8_PPAT(1, GEN8_PPAT_WC | GEN8_PPAT_LLCELLC) |	/* for something pointing to ptes? */
 	      GEN8_PPAT(3, GEN8_PPAT_UC) |			/* Uncached objects, mostly for scanout */
 	      GEN8_PPAT(4, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(0)) |
 	      GEN8_PPAT(5, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(1)) |
 	      GEN8_PPAT(6, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(2)) |
 	      GEN8_PPAT(7, GEN8_PPAT_WB | GEN8_PPAT_LLCELLC | GEN8_PPAT_AGE(3));

 	/* for scanout with eLLC */
 	if (INTEL_GEN(i915) >= 9)
 		pat |= GEN8_PPAT(2, GEN8_PPAT_WB | GEN8_PPAT_ELLC_OVERRIDE);
 	else
 		pat |= GEN8_PPAT(2, GEN8_PPAT_WT | GEN8_PPAT_LLCELLC);

 	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_LO, lower_32_bits(pat));
 	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_HI, upper_32_bits(pat));
 }

 static void chv_setup_private_ppat(struct intel_uncore *uncore)
 {
 	u64 pat;

 	/*
 	 * Map WB on BDW to snooped on CHV.
 	 *
 	 * Only the snoop bit has meaning for CHV, the rest is
 	 * ignored.
 	 *
 	 * The hardware will never snoop for certain types of accesses:
 	 * - CPU GTT (GMADR->GGTT->no snoop->memory)
 	 * - PPGTT page tables
 	 * - some other special cycles
 	 *
 	 * As with BDW, we also need to consider the following for GT accesses:
 	 * "For GGTT, there is NO pat_sel[2:0] from the entry,
 	 * so RTL will always use the value corresponding to
 	 * pat_sel = 000".
 	 * Which means we must set the snoop bit in PAT entry 0
 	 * in order to keep the global status page working.
 	 */

 	pat = GEN8_PPAT(0, CHV_PPAT_SNOOP) |
 	      GEN8_PPAT(1, 0) |
 	      GEN8_PPAT(2, 0) |
 	      GEN8_PPAT(3, 0) |
 	      GEN8_PPAT(4, CHV_PPAT_SNOOP) |
 	      GEN8_PPAT(5, CHV_PPAT_SNOOP) |
 	      GEN8_PPAT(6, CHV_PPAT_SNOOP) |
 	      GEN8_PPAT(7, CHV_PPAT_SNOOP);

 	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_LO, lower_32_bits(pat));
 	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_HI, upper_32_bits(pat));
 }

 void setup_private_pat(struct intel_uncore *uncore)
 {
 	struct drm_i915_private *i915 = uncore->i915;

 	GEM_BUG_ON(INTEL_GEN(i915) < 8);

 	if (INTEL_GEN(i915) >= 12)
 		tgl_setup_private_ppat(uncore);
 	else if (INTEL_GEN(i915) >= 10)
 		cnl_setup_private_ppat(uncore);
 	else if (IS_CHERRYVIEW(i915) || IS_GEN9_LP(i915))
 		chv_setup_private_ppat(uncore);
 	else
 		bdw_setup_private_ppat(uncore);
 }

 struct i915_vma *
 __vm_create_scratch_for_read(struct i915_address_space *vm, unsigned long size)
 {
 	struct drm_i915_gem_object *obj;
 	struct i915_vma *vma;
 	int err;

 	obj = i915_gem_object_create_internal(vm->i915, PAGE_ALIGN(size));
 	if (IS_ERR(obj))
 		return ERR_CAST(obj);

 	i915_gem_object_set_cache_coherency(obj, I915_CACHING_CACHED);

 	vma = i915_vma_instance(obj, vm, NULL);
 	if (IS_ERR(vma)) {
 		i915_gem_object_put(obj);
 		return vma;
 	}

 	err = i915_vma_pin(vma, 0, 0,
 			   i915_vma_is_ggtt(vma) ? PIN_GLOBAL : PIN_USER);
 	if (err) {
 		i915_vma_put(vma);
 		return ERR_PTR(err);
 	}

 	return vma;
 }

 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/mock_gtt.c"
 #endif
	// SPDX-License-Identifier: MIT
	/*
	* Copyright © 2020 Intel Corporation
	*/

	#include <linux/slab.h> /* fault-inject.h is not standalone! */

	#include <linux/fault-inject.h>

	#include "i915_trace.h"
	#include "intel_gt.h"
	#include "intel_gtt.h"

	struct drm_i915_gem_object alloc_pt_dma(struct i915_address_space vm, int sz)
	{
	if (I915_SELFTEST_ONLY(should_fail(&vm->fault_attr, 1)))
	i915_gem_shrink_all(vm->i915);

	return i915_gem_object_create_internal(vm->i915, sz);
	}

	int pin_pt_dma(struct i915_address_space vm, struct drm_i915_gem_object obj)
	{
	int err;

	err = i915_gem_object_pin_pages(obj);
	if (err)
	return err;

	i915_gem_object_make_unshrinkable(obj);
	return 0;
	}

	void __i915_vm_close(struct i915_address_space *vm)
	{
	struct i915_vma vma, vn;

	if (!atomic_dec_and_mutex_lock(&vm->open, &vm->mutex))
	return;

	list_for_each_entry_safe(vma, vn, &vm->bound_list, vm_link) {
	struct drm_i915_gem_object *obj = vma->obj;

	/* Keep the obj (and hence the vma) alive as _we_ destroy it */
	if (!kref_get_unless_zero(&obj->base.refcount))
	continue;

	atomic_and(~I915_VMA_PIN_MASK, &vma->flags);
	WARN_ON(__i915_vma_unbind(vma));
	__i915_vma_put(vma);

	i915_gem_object_put(obj);
	}
	GEM_BUG_ON(!list_empty(&vm->bound_list));

	mutex_unlock(&vm->mutex);
	}

	void i915_address_space_fini(struct i915_address_space *vm)
	{
	drm_mm_takedown(&vm->mm);
	mutex_destroy(&vm->mutex);
	}

	static void __i915_vm_release(struct work_struct *work)
	{
	struct i915_address_space *vm =
	container_of(work, struct i915_address_space, rcu.work);

	vm->cleanup(vm);
	i915_address_space_fini(vm);

	kfree(vm);
	}

	void i915_vm_release(struct kref *kref)
	{
	struct i915_address_space *vm =
	container_of(kref, struct i915_address_space, ref);

	GEM_BUG_ON(i915_is_ggtt(vm));
	trace_i915_ppgtt_release(vm);

	queue_rcu_work(vm->i915->wq, &vm->rcu);
	}

	void i915_address_space_init(struct i915_address_space *vm, int subclass)
	{
	kref_init(&vm->ref);
	INIT_RCU_WORK(&vm->rcu, __i915_vm_release);
	atomic_set(&vm->open, 1);

	/*
	* The vm->mutex must be reclaim safe (for use in the shrinker).
	* Do a dummy acquire now under fs_reclaim so that any allocation
	* attempt holding the lock is immediately reported by lockdep.
	*/
	mutex_init(&vm->mutex);
	lockdep_set_subclass(&vm->mutex, subclass);
	i915_gem_shrinker_taints_mutex(vm->i915, &vm->mutex);

	GEM_BUG_ON(!vm->total);
	drm_mm_init(&vm->mm, 0, vm->total);
	vm->mm.head_node.color = I915_COLOR_UNEVICTABLE;

	INIT_LIST_HEAD(&vm->bound_list);
	}

	void clear_pages(struct i915_vma *vma)
	{
	GEM_BUG_ON(!vma->pages);

	if (vma->pages != vma->obj->mm.pages) {
	sg_free_table(vma->pages);
	kfree(vma->pages);
	}
	vma->pages = NULL;

	memset(&vma->page_sizes, 0, sizeof(vma->page_sizes));
	}

	dma_addr_t __px_dma(struct drm_i915_gem_object *p)
	{
	GEM_BUG_ON(!i915_gem_object_has_pages(p));
	return sg_dma_address(p->mm.pages->sgl);
	}

	struct page __px_page(struct drm_i915_gem_object p)
	{
	GEM_BUG_ON(!i915_gem_object_has_pages(p));
	return sg_page(p->mm.pages->sgl);
	}

	void
	fill_page_dma(struct drm_i915_gem_object *p, const u64 val, unsigned int count)
	{
	struct page *page = __px_page(p);
	void *vaddr;

	vaddr = kmap(page);
	memset64(vaddr, val, count);
	clflush_cache_range(vaddr, PAGE_SIZE);
	kunmap(page);
	}

	static void poison_scratch_page(struct drm_i915_gem_object *scratch)
	{
	struct sgt_iter sgt;
	struct page *page;
	u8 val;

	val = 0;
	if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
	val = POISON_FREE;

	for_each_sgt_page(page, sgt, scratch->mm.pages) {
	void *vaddr;

	vaddr = kmap(page);
	memset(vaddr, val, PAGE_SIZE);
	kunmap(page);
	}
	}

	int setup_scratch_page(struct i915_address_space *vm)
	{
	unsigned long size;

	/*
	* In order to utilize 64K pages for an object with a size < 2M, we will
	* need to support a 64K scratch page, given that every 16th entry for a
	* page-table operating in 64K mode must point to a properly aligned 64K
	* region, including any PTEs which happen to point to scratch.
	*
	* This is only relevant for the 48b PPGTT where we support
	* huge-gtt-pages, see also i915_vma_insert(). However, as we share the
	* scratch (read-only) between all vm, we create one 64k scratch page
	* for all.
	*/
	size = I915_GTT_PAGE_SIZE_4K;
	if (i915_vm_is_4lvl(vm) &&
	HAS_PAGE_SIZES(vm->i915, I915_GTT_PAGE_SIZE_64K))
	size = I915_GTT_PAGE_SIZE_64K;

	do {
	struct drm_i915_gem_object *obj;

	obj = vm->alloc_pt_dma(vm, size);
	if (IS_ERR(obj))
	goto skip;

	if (pin_pt_dma(vm, obj))
	goto skip_obj;

	/* We need a single contiguous page for our scratch */
	if (obj->mm.page_sizes.sg < size)
	goto skip_obj;

	/* And it needs to be correspondingly aligned */
	if (__px_dma(obj) & (size - 1))
	goto skip_obj;

	/*
	* Use a non-zero scratch page for debugging.
	*
	* We want a value that should be reasonably obvious
	* to spot in the error state, while also causing a GPU hang
	* if executed. We prefer using a clear page in production, so
	* should it ever be accidentally used, the effect should be
	* fairly benign.
	*/
	poison_scratch_page(obj);

	vm->scratch[0] = obj;
	vm->scratch_order = get_order(size);
	return 0;

	skip_obj:
	i915_gem_object_put(obj);
	skip:
	if (size == I915_GTT_PAGE_SIZE_4K)
	return -ENOMEM;

	size = I915_GTT_PAGE_SIZE_4K;
	} while (1);
	}

	void free_scratch(struct i915_address_space *vm)
	{
	int i;

	for (i = 0; i <= vm->top; i++)
	i915_gem_object_put(vm->scratch[i]);
	}

	void gtt_write_workarounds(struct intel_gt *gt)
	{
	struct drm_i915_private *i915 = gt->i915;
	struct intel_uncore *uncore = gt->uncore;

	/*
	* This function is for gtt related workarounds. This function is
	* called on driver load and after a GPU reset, so you can place
	* workarounds here even if they get overwritten by GPU reset.
	*/
	/* WaIncreaseDefaultTLBEntries:chv,bdw,skl,bxt,kbl,glk,cfl,cnl,icl */
	if (IS_BROADWELL(i915))
	intel_uncore_write(uncore,
	GEN8_L3_LRA_1_GPGPU,
	GEN8_L3_LRA_1_GPGPU_DEFAULT_VALUE_BDW);
	else if (IS_CHERRYVIEW(i915))
	intel_uncore_write(uncore,
	GEN8_L3_LRA_1_GPGPU,
	GEN8_L3_LRA_1_GPGPU_DEFAULT_VALUE_CHV);
	else if (IS_GEN9_LP(i915))
	intel_uncore_write(uncore,
	GEN8_L3_LRA_1_GPGPU,
	GEN9_L3_LRA_1_GPGPU_DEFAULT_VALUE_BXT);
	else if (INTEL_GEN(i915) >= 9 && INTEL_GEN(i915) <= 11)
	intel_uncore_write(uncore,
	GEN8_L3_LRA_1_GPGPU,
	GEN9_L3_LRA_1_GPGPU_DEFAULT_VALUE_SKL);

	/*
	* To support 64K PTEs we need to first enable the use of the
	* Intermediate-Page-Size(IPS) bit of the PDE field via some magical
	* mmio, otherwise the page-walker will simply ignore the IPS bit. This
	* shouldn't be needed after GEN10.
	*
	* 64K pages were first introduced from BDW+, although technically they
	* only work from gen9+. For pre-BDW we instead have the option for
	* 32K pages, but we don't currently have any support for it in our
	* driver.
	*/
	if (HAS_PAGE_SIZES(i915, I915_GTT_PAGE_SIZE_64K) &&
	INTEL_GEN(i915) <= 10)
	intel_uncore_rmw(uncore,
	GEN8_GAMW_ECO_DEV_RW_IA,
	0,
	GAMW_ECO_ENABLE_64K_IPS_FIELD);

	if (IS_GEN_RANGE(i915, 8, 11)) {
	bool can_use_gtt_cache = true;

	/*
	* According to the BSpec if we use 2M/1G pages then we also
	* need to disable the GTT cache. At least on BDW we can see
	* visual corruption when using 2M pages, and not disabling the
	* GTT cache.
	*/
	if (HAS_PAGE_SIZES(i915, I915_GTT_PAGE_SIZE_2M))
	can_use_gtt_cache = false;

	/* WaGttCachingOffByDefault */
	intel_uncore_write(uncore,
	HSW_GTT_CACHE_EN,
	can_use_gtt_cache ? GTT_CACHE_EN_ALL : 0);
	drm_WARN_ON_ONCE(&i915->drm, can_use_gtt_cache &&
	intel_uncore_read(uncore,
	HSW_GTT_CACHE_EN) == 0);
	}
	}

	static void tgl_setup_private_ppat(struct intel_uncore *uncore)
	{
	/* TGL doesn't support LLC or AGE settings */
	intel_uncore_write(uncore, GEN12_PAT_INDEX(0), GEN8_PPAT_WB);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(1), GEN8_PPAT_WC);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(2), GEN8_PPAT_WT);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(3), GEN8_PPAT_UC);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(4), GEN8_PPAT_WB);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(5), GEN8_PPAT_WB);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(6), GEN8_PPAT_WB);
	intel_uncore_write(uncore, GEN12_PAT_INDEX(7), GEN8_PPAT_WB);
	}

	static void cnl_setup_private_ppat(struct intel_uncore *uncore)
	{
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(0),
	GEN8_PPAT_WB \| GEN8_PPAT_LLC);
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(1),
	GEN8_PPAT_WC \| GEN8_PPAT_LLCELLC);
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(2),
	GEN8_PPAT_WB \| GEN8_PPAT_ELLC_OVERRIDE);
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(3),
	GEN8_PPAT_UC);
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(4),
	GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(0));
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(5),
	GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(1));
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(6),
	GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(2));
	intel_uncore_write(uncore,
	GEN10_PAT_INDEX(7),
	GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(3));
	}

	/*
	* The GGTT and PPGTT need a private PPAT setup in order to handle cacheability
	* bits. When using advanced contexts each context stores its own PAT, but
	* writing this data shouldn't be harmful even in those cases.
	*/
	static void bdw_setup_private_ppat(struct intel_uncore *uncore)
	{
	struct drm_i915_private *i915 = uncore->i915;
	u64 pat;

	pat = GEN8_PPAT(0, GEN8_PPAT_WB \| GEN8_PPAT_LLC) \| /* for normal objects, no eLLC */
	GEN8_PPAT(1, GEN8_PPAT_WC \| GEN8_PPAT_LLCELLC) \| /* for something pointing to ptes? */
	GEN8_PPAT(3, GEN8_PPAT_UC) \| /* Uncached objects, mostly for scanout */
	GEN8_PPAT(4, GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(0)) \|
	GEN8_PPAT(5, GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(1)) \|
	GEN8_PPAT(6, GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(2)) \|
	GEN8_PPAT(7, GEN8_PPAT_WB \| GEN8_PPAT_LLCELLC \| GEN8_PPAT_AGE(3));

	/* for scanout with eLLC */
	if (INTEL_GEN(i915) >= 9)
	pat \|= GEN8_PPAT(2, GEN8_PPAT_WB \| GEN8_PPAT_ELLC_OVERRIDE);
	else
	pat \|= GEN8_PPAT(2, GEN8_PPAT_WT \| GEN8_PPAT_LLCELLC);

	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_LO, lower_32_bits(pat));
	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_HI, upper_32_bits(pat));
	}

	static void chv_setup_private_ppat(struct intel_uncore *uncore)
	{
	u64 pat;

	/*
	* Map WB on BDW to snooped on CHV.
	*
	* Only the snoop bit has meaning for CHV, the rest is
	* ignored.
	*
	* The hardware will never snoop for certain types of accesses:
	* - CPU GTT (GMADR->GGTT->no snoop->memory)
	* - PPGTT page tables
	* - some other special cycles
	*
	* As with BDW, we also need to consider the following for GT accesses:
	* "For GGTT, there is NO pat_sel[2:0] from the entry,
	* so RTL will always use the value corresponding to
	* pat_sel = 000".
	* Which means we must set the snoop bit in PAT entry 0
	* in order to keep the global status page working.
	*/

	pat = GEN8_PPAT(0, CHV_PPAT_SNOOP) \|
	GEN8_PPAT(1, 0) \|
	GEN8_PPAT(2, 0) \|
	GEN8_PPAT(3, 0) \|
	GEN8_PPAT(4, CHV_PPAT_SNOOP) \|
	GEN8_PPAT(5, CHV_PPAT_SNOOP) \|
	GEN8_PPAT(6, CHV_PPAT_SNOOP) \|
	GEN8_PPAT(7, CHV_PPAT_SNOOP);

	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_LO, lower_32_bits(pat));
	intel_uncore_write(uncore, GEN8_PRIVATE_PAT_HI, upper_32_bits(pat));
	}

	void setup_private_pat(struct intel_uncore *uncore)
	{
	struct drm_i915_private *i915 = uncore->i915;

	GEM_BUG_ON(INTEL_GEN(i915) < 8);

	if (INTEL_GEN(i915) >= 12)
	tgl_setup_private_ppat(uncore);
	else if (INTEL_GEN(i915) >= 10)
	cnl_setup_private_ppat(uncore);
	else if (IS_CHERRYVIEW(i915) \|\| IS_GEN9_LP(i915))
	chv_setup_private_ppat(uncore);
	else
	bdw_setup_private_ppat(uncore);
	}

	struct i915_vma *
	__vm_create_scratch_for_read(struct i915_address_space *vm, unsigned long size)
	{
	struct drm_i915_gem_object *obj;
	struct i915_vma *vma;
	int err;

	obj = i915_gem_object_create_internal(vm->i915, PAGE_ALIGN(size));
	if (IS_ERR(obj))
	return ERR_CAST(obj);

	i915_gem_object_set_cache_coherency(obj, I915_CACHING_CACHED);

	vma = i915_vma_instance(obj, vm, NULL);
	if (IS_ERR(vma)) {
	i915_gem_object_put(obj);
	return vma;
	}

	err = i915_vma_pin(vma, 0, 0,
	i915_vma_is_ggtt(vma) ? PIN_GLOBAL : PIN_USER);
	if (err) {
	i915_vma_put(vma);
	return ERR_PTR(err);
	}

	return vma;
	}

	#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
	#include "selftests/mock_gtt.c"
	#endif