drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c - linux - Git at Google

 /*
  * SPDX-License-Identifier: MIT
  *
  * Copyright © 2017 Intel Corporation
  */

 #include <linux/prime_numbers.h>

 #include "gt/intel_engine_pm.h"
 #include "gt/intel_gpu_commands.h"
 #include "gt/intel_gt.h"
 #include "gt/intel_gt_pm.h"
 #include "gt/intel_ring.h"

 #include "i915_selftest.h"
 #include "selftests/i915_random.h"

 struct context {
 	struct drm_i915_gem_object *obj;
 	struct intel_engine_cs *engine;
 };

 static int cpu_set(struct context *ctx, unsigned long offset, u32 v)
 {
 	unsigned int needs_clflush;
 	struct page *page;
 	u32 *cpu;
 	int err;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_prepare_write(ctx->obj, &needs_clflush);
 	if (err)
 		goto out;

 	page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
 	cpu = kmap_local_page(page) + offset_in_page(offset);

 	if (needs_clflush & CLFLUSH_BEFORE)
 		drm_clflush_virt_range(cpu, sizeof(*cpu));

 	*cpu = v;

 	if (needs_clflush & CLFLUSH_AFTER)
 		drm_clflush_virt_range(cpu, sizeof(*cpu));

 	kunmap_local(cpu);
 	i915_gem_object_finish_access(ctx->obj);

 out:
 	i915_gem_object_unlock(ctx->obj);
 	return err;
 }

 static int cpu_get(struct context *ctx, unsigned long offset, u32 *v)
 {
 	unsigned int needs_clflush;
 	struct page *page;
 	u32 *cpu;
 	int err;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_prepare_read(ctx->obj, &needs_clflush);
 	if (err)
 		goto out;

 	page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
 	cpu = kmap_local_page(page) + offset_in_page(offset);

 	if (needs_clflush & CLFLUSH_BEFORE)
 		drm_clflush_virt_range(cpu, sizeof(*cpu));

 	*v = *cpu;

 	kunmap_local(cpu);
 	i915_gem_object_finish_access(ctx->obj);

 out:
 	i915_gem_object_unlock(ctx->obj);
 	return err;
 }

 static int gtt_set(struct context *ctx, unsigned long offset, u32 v)
 {
 	intel_wakeref_t wakeref;
 	struct i915_vma *vma;
 	u32 __iomem *map;
 	int err = 0;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
 	i915_gem_object_unlock(ctx->obj);
 	if (err)
 		return err;

 	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, PIN_MAPPABLE);
 	if (IS_ERR(vma))
 		return PTR_ERR(vma);

 	wakeref = intel_gt_pm_get(vma->vm->gt);

 	map = i915_vma_pin_iomap(vma);
 	i915_vma_unpin(vma);
 	if (IS_ERR(map)) {
 		err = PTR_ERR(map);
 		goto out_rpm;
 	}

 	iowrite32(v, &map[offset / sizeof(*map)]);
 	i915_vma_unpin_iomap(vma);

 out_rpm:
 	intel_gt_pm_put(vma->vm->gt, wakeref);
 	return err;
 }

 static int gtt_get(struct context *ctx, unsigned long offset, u32 *v)
 {
 	intel_wakeref_t wakeref;
 	struct i915_vma *vma;
 	u32 __iomem *map;
 	int err = 0;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_set_to_gtt_domain(ctx->obj, false);
 	i915_gem_object_unlock(ctx->obj);
 	if (err)
 		return err;

 	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, PIN_MAPPABLE);
 	if (IS_ERR(vma))
 		return PTR_ERR(vma);

 	wakeref = intel_gt_pm_get(vma->vm->gt);

 	map = i915_vma_pin_iomap(vma);
 	i915_vma_unpin(vma);
 	if (IS_ERR(map)) {
 		err = PTR_ERR(map);
 		goto out_rpm;
 	}

 	*v = ioread32(&map[offset / sizeof(*map)]);
 	i915_vma_unpin_iomap(vma);

 out_rpm:
 	intel_gt_pm_put(vma->vm->gt, wakeref);
 	return err;
 }

 static int wc_set(struct context *ctx, unsigned long offset, u32 v)
 {
 	u32 *map;
 	int err;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_set_to_wc_domain(ctx->obj, true);
 	i915_gem_object_unlock(ctx->obj);
 	if (err)
 		return err;

 	map = i915_gem_object_pin_map_unlocked(ctx->obj, I915_MAP_WC);
 	if (IS_ERR(map))
 		return PTR_ERR(map);

 	map[offset / sizeof(*map)] = v;

 	__i915_gem_object_flush_map(ctx->obj, offset, sizeof(*map));
 	i915_gem_object_unpin_map(ctx->obj);

 	return 0;
 }

 static int wc_get(struct context *ctx, unsigned long offset, u32 *v)
 {
 	u32 *map;
 	int err;

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_set_to_wc_domain(ctx->obj, false);
 	i915_gem_object_unlock(ctx->obj);
 	if (err)
 		return err;

 	map = i915_gem_object_pin_map_unlocked(ctx->obj, I915_MAP_WC);
 	if (IS_ERR(map))
 		return PTR_ERR(map);

 	*v = map[offset / sizeof(*map)];
 	i915_gem_object_unpin_map(ctx->obj);

 	return 0;
 }

 static int gpu_set(struct context *ctx, unsigned long offset, u32 v)
 {
 	struct i915_request *rq;
 	struct i915_vma *vma;
 	u32 *cs;
 	int err;

 	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, 0);
 	if (IS_ERR(vma))
 		return PTR_ERR(vma);

 	i915_gem_object_lock(ctx->obj, NULL);
 	err = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
 	if (err)
 		goto out_unlock;

 	rq = intel_engine_create_kernel_request(ctx->engine);
 	if (IS_ERR(rq)) {
 		err = PTR_ERR(rq);
 		goto out_unpin;
 	}

 	cs = intel_ring_begin(rq, 4);
 	if (IS_ERR(cs)) {
 		err = PTR_ERR(cs);
 		goto out_rq;
 	}

 	if (GRAPHICS_VER(ctx->engine->i915) >= 8) {
 		*cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
 		*cs++ = lower_32_bits(i915_ggtt_offset(vma) + offset);
 		*cs++ = upper_32_bits(i915_ggtt_offset(vma) + offset);
 		*cs++ = v;
 	} else if (GRAPHICS_VER(ctx->engine->i915) >= 4) {
 		*cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
 		*cs++ = 0;
 		*cs++ = i915_ggtt_offset(vma) + offset;
 		*cs++ = v;
 	} else {
 		*cs++ = MI_STORE_DWORD_IMM | MI_MEM_VIRTUAL;
 		*cs++ = i915_ggtt_offset(vma) + offset;
 		*cs++ = v;
 		*cs++ = MI_NOOP;
 	}
 	intel_ring_advance(rq, cs);

 	err = i915_vma_move_to_active(vma, rq, EXEC_OBJECT_WRITE);

 out_rq:
 	i915_request_add(rq);
 out_unpin:
 	i915_vma_unpin(vma);
 out_unlock:
 	i915_gem_object_unlock(ctx->obj);

 	return err;
 }

 static bool always_valid(struct context *ctx)
 {
 	return true;
 }

 static bool needs_fence_registers(struct context *ctx)
 {
 	struct intel_gt *gt = ctx->engine->gt;

 	if (intel_gt_is_wedged(gt))
 		return false;

 	return gt->ggtt->num_fences;
 }

 static bool needs_mi_store_dword(struct context *ctx)
 {
 	if (intel_gt_is_wedged(ctx->engine->gt))
 		return false;

 	return intel_engine_can_store_dword(ctx->engine);
 }

 static const struct igt_coherency_mode {
 	const char *name;
 	int (*set)(struct context *ctx, unsigned long offset, u32 v);
 	int (*get)(struct context *ctx, unsigned long offset, u32 *v);
 	bool (*valid)(struct context *ctx);
 } igt_coherency_mode[] = {
 	{ "cpu", cpu_set, cpu_get, always_valid },
 	{ "gtt", gtt_set, gtt_get, needs_fence_registers },
 	{ "wc", wc_set, wc_get, always_valid },
 	{ "gpu", gpu_set, NULL, needs_mi_store_dword },
 	{ },
 };

 static struct intel_engine_cs *
 random_engine(struct drm_i915_private *i915, struct rnd_state *prng)
 {
 	struct intel_engine_cs *engine;
 	unsigned int count;

 	count = 0;
 	for_each_uabi_engine(engine, i915)
 		count++;

 	count = i915_prandom_u32_max_state(count, prng);
 	for_each_uabi_engine(engine, i915)
 		if (count-- == 0)
 			return engine;

 	return NULL;
 }

 static int igt_gem_coherency(void *arg)
 {
 	const unsigned int ncachelines = PAGE_SIZE/64;
 	struct drm_i915_private *i915 = arg;
 	const struct igt_coherency_mode *read, *write, *over;
 	unsigned long count, n;
 	u32 *offsets, *values;
 	I915_RND_STATE(prng);
 	struct context ctx;
 	int err = 0;

 	/*
 	 * We repeatedly write, overwrite and read from a sequence of
 	 * cachelines in order to try and detect incoherency (unflushed writes
 	 * from either the CPU or GPU). Each setter/getter uses our cache
 	 * domain API which should prevent incoherency.
 	 */

 	offsets = kmalloc_array(ncachelines, 2*sizeof(u32), GFP_KERNEL);
 	if (!offsets)
 		return -ENOMEM;
 	for (count = 0; count < ncachelines; count++)
 		offsets[count] = count * 64 + 4 * (count % 16);

 	values = offsets + ncachelines;

 	ctx.engine = random_engine(i915, &prng);
 	if (!ctx.engine) {
 		err = -ENODEV;
 		goto out_free;
 	}
 	pr_info("%s: using %s\n", __func__, ctx.engine->name);
 	intel_engine_pm_get(ctx.engine);

 	for (over = igt_coherency_mode; over->name; over++) {
 		if (!over->set)
 			continue;

 		if (!over->valid(&ctx))
 			continue;

 		for (write = igt_coherency_mode; write->name; write++) {
 			if (!write->set)
 				continue;

 			if (!write->valid(&ctx))
 				continue;

 			for (read = igt_coherency_mode; read->name; read++) {
 				if (!read->get)
 					continue;

 				if (!read->valid(&ctx))
 					continue;

 				for_each_prime_number_from(count, 1, ncachelines) {
 					ctx.obj = i915_gem_object_create_internal(i915, PAGE_SIZE);
 					if (IS_ERR(ctx.obj)) {
 						err = PTR_ERR(ctx.obj);
 						goto out_pm;
 					}

 					i915_random_reorder(offsets, ncachelines, &prng);
 					for (n = 0; n < count; n++)
 						values[n] = prandom_u32_state(&prng);

 					for (n = 0; n < count; n++) {
 						err = over->set(&ctx, offsets[n], ~values[n]);
 						if (err) {
 							pr_err("Failed to set stale value[%ld/%ld] in object using %s, err=%d\n",
 							       n, count, over->name, err);
 							goto put_object;
 						}
 					}

 					for (n = 0; n < count; n++) {
 						err = write->set(&ctx, offsets[n], values[n]);
 						if (err) {
 							pr_err("Failed to set value[%ld/%ld] in object using %s, err=%d\n",
 							       n, count, write->name, err);
 							goto put_object;
 						}
 					}

 					for (n = 0; n < count; n++) {
 						u32 found;

 						err = read->get(&ctx, offsets[n], &found);
 						if (err) {
 							pr_err("Failed to get value[%ld/%ld] in object using %s, err=%d\n",
 							       n, count, read->name, err);
 							goto put_object;
 						}

 						if (found != values[n]) {
 							pr_err("Value[%ld/%ld] mismatch, (overwrite with %s) wrote [%s] %x read [%s] %x (inverse %x), at offset %x\n",
 							       n, count, over->name,
 							       write->name, values[n],
 							       read->name, found,
 							       ~values[n], offsets[n]);
 							err = -EINVAL;
 							goto put_object;
 						}
 					}

 					i915_gem_object_put(ctx.obj);
 				}
 			}
 		}
 	}
 out_pm:
 	intel_engine_pm_put(ctx.engine);
 out_free:
 	kfree(offsets);
 	return err;

 put_object:
 	i915_gem_object_put(ctx.obj);
 	goto out_pm;
 }

 int i915_gem_coherency_live_selftests(struct drm_i915_private *i915)
 {
 	static const struct i915_subtest tests[] = {
 		SUBTEST(igt_gem_coherency),
 	};

 	return i915_live_subtests(tests, i915);
 }
	/*
	* SPDX-License-Identifier: MIT
	*
	* Copyright © 2017 Intel Corporation
	*/

	#include <linux/prime_numbers.h>

	#include "gt/intel_engine_pm.h"
	#include "gt/intel_gpu_commands.h"
	#include "gt/intel_gt.h"
	#include "gt/intel_gt_pm.h"
	#include "gt/intel_ring.h"

	#include "i915_selftest.h"
	#include "selftests/i915_random.h"

	struct context {
	struct drm_i915_gem_object *obj;
	struct intel_engine_cs *engine;
	};

	static int cpu_set(struct context *ctx, unsigned long offset, u32 v)
	{
	unsigned int needs_clflush;
	struct page *page;
	u32 *cpu;
	int err;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_prepare_write(ctx->obj, &needs_clflush);
	if (err)
	goto out;

	page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
	cpu = kmap_local_page(page) + offset_in_page(offset);

	if (needs_clflush & CLFLUSH_BEFORE)
	drm_clflush_virt_range(cpu, sizeof(*cpu));

	*cpu = v;

	if (needs_clflush & CLFLUSH_AFTER)
	drm_clflush_virt_range(cpu, sizeof(*cpu));

	kunmap_local(cpu);
	i915_gem_object_finish_access(ctx->obj);

	out:
	i915_gem_object_unlock(ctx->obj);
	return err;
	}

	static int cpu_get(struct context ctx, unsigned long offset, u32 v)
	{
	unsigned int needs_clflush;
	struct page *page;
	u32 *cpu;
	int err;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_prepare_read(ctx->obj, &needs_clflush);
	if (err)
	goto out;

	page = i915_gem_object_get_page(ctx->obj, offset >> PAGE_SHIFT);
	cpu = kmap_local_page(page) + offset_in_page(offset);

	if (needs_clflush & CLFLUSH_BEFORE)
	drm_clflush_virt_range(cpu, sizeof(*cpu));

	v = cpu;

	kunmap_local(cpu);
	i915_gem_object_finish_access(ctx->obj);

	out:
	i915_gem_object_unlock(ctx->obj);
	return err;
	}

	static int gtt_set(struct context *ctx, unsigned long offset, u32 v)
	{
	intel_wakeref_t wakeref;
	struct i915_vma *vma;
	u32 __iomem *map;
	int err = 0;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
	i915_gem_object_unlock(ctx->obj);
	if (err)
	return err;

	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, PIN_MAPPABLE);
	if (IS_ERR(vma))
	return PTR_ERR(vma);

	wakeref = intel_gt_pm_get(vma->vm->gt);

	map = i915_vma_pin_iomap(vma);
	i915_vma_unpin(vma);
	if (IS_ERR(map)) {
	err = PTR_ERR(map);
	goto out_rpm;
	}

	iowrite32(v, &map[offset / sizeof(*map)]);
	i915_vma_unpin_iomap(vma);

	out_rpm:
	intel_gt_pm_put(vma->vm->gt, wakeref);
	return err;
	}

	static int gtt_get(struct context ctx, unsigned long offset, u32 v)
	{
	intel_wakeref_t wakeref;
	struct i915_vma *vma;
	u32 __iomem *map;
	int err = 0;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_set_to_gtt_domain(ctx->obj, false);
	i915_gem_object_unlock(ctx->obj);
	if (err)
	return err;

	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, PIN_MAPPABLE);
	if (IS_ERR(vma))
	return PTR_ERR(vma);

	wakeref = intel_gt_pm_get(vma->vm->gt);

	map = i915_vma_pin_iomap(vma);
	i915_vma_unpin(vma);
	if (IS_ERR(map)) {
	err = PTR_ERR(map);
	goto out_rpm;
	}

	v = ioread32(&map[offset / sizeof(map)]);
	i915_vma_unpin_iomap(vma);

	out_rpm:
	intel_gt_pm_put(vma->vm->gt, wakeref);
	return err;
	}

	static int wc_set(struct context *ctx, unsigned long offset, u32 v)
	{
	u32 *map;
	int err;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_set_to_wc_domain(ctx->obj, true);
	i915_gem_object_unlock(ctx->obj);
	if (err)
	return err;

	map = i915_gem_object_pin_map_unlocked(ctx->obj, I915_MAP_WC);
	if (IS_ERR(map))
	return PTR_ERR(map);

	map[offset / sizeof(*map)] = v;

	__i915_gem_object_flush_map(ctx->obj, offset, sizeof(*map));
	i915_gem_object_unpin_map(ctx->obj);

	return 0;
	}

	static int wc_get(struct context ctx, unsigned long offset, u32 v)
	{
	u32 *map;
	int err;

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_set_to_wc_domain(ctx->obj, false);
	i915_gem_object_unlock(ctx->obj);
	if (err)
	return err;

	map = i915_gem_object_pin_map_unlocked(ctx->obj, I915_MAP_WC);
	if (IS_ERR(map))
	return PTR_ERR(map);

	v = map[offset / sizeof(map)];
	i915_gem_object_unpin_map(ctx->obj);

	return 0;
	}

	static int gpu_set(struct context *ctx, unsigned long offset, u32 v)
	{
	struct i915_request *rq;
	struct i915_vma *vma;
	u32 *cs;
	int err;

	vma = i915_gem_object_ggtt_pin(ctx->obj, NULL, 0, 0, 0);
	if (IS_ERR(vma))
	return PTR_ERR(vma);

	i915_gem_object_lock(ctx->obj, NULL);
	err = i915_gem_object_set_to_gtt_domain(ctx->obj, true);
	if (err)
	goto out_unlock;

	rq = intel_engine_create_kernel_request(ctx->engine);
	if (IS_ERR(rq)) {
	err = PTR_ERR(rq);
	goto out_unpin;
	}

	cs = intel_ring_begin(rq, 4);
	if (IS_ERR(cs)) {
	err = PTR_ERR(cs);
	goto out_rq;
	}

	if (GRAPHICS_VER(ctx->engine->i915) >= 8) {
	*cs++ = MI_STORE_DWORD_IMM_GEN4 \| MI_USE_GGTT;
	*cs++ = lower_32_bits(i915_ggtt_offset(vma) + offset);
	*cs++ = upper_32_bits(i915_ggtt_offset(vma) + offset);
	*cs++ = v;
	} else if (GRAPHICS_VER(ctx->engine->i915) >= 4) {
	*cs++ = MI_STORE_DWORD_IMM_GEN4 \| MI_USE_GGTT;
	*cs++ = 0;
	*cs++ = i915_ggtt_offset(vma) + offset;
	*cs++ = v;
	} else {
	*cs++ = MI_STORE_DWORD_IMM \| MI_MEM_VIRTUAL;
	*cs++ = i915_ggtt_offset(vma) + offset;
	*cs++ = v;
	*cs++ = MI_NOOP;
	}
	intel_ring_advance(rq, cs);

	err = i915_vma_move_to_active(vma, rq, EXEC_OBJECT_WRITE);

	out_rq:
	i915_request_add(rq);
	out_unpin:
	i915_vma_unpin(vma);
	out_unlock:
	i915_gem_object_unlock(ctx->obj);

	return err;
	}

	static bool always_valid(struct context *ctx)
	{
	return true;
	}

	static bool needs_fence_registers(struct context *ctx)
	{
	struct intel_gt *gt = ctx->engine->gt;

	if (intel_gt_is_wedged(gt))
	return false;

	return gt->ggtt->num_fences;
	}

	static bool needs_mi_store_dword(struct context *ctx)
	{
	if (intel_gt_is_wedged(ctx->engine->gt))
	return false;

	return intel_engine_can_store_dword(ctx->engine);
	}

	static const struct igt_coherency_mode {
	const char *name;
	int (set)(struct context ctx, unsigned long offset, u32 v);
	int (get)(struct context ctx, unsigned long offset, u32 *v);
	bool (valid)(struct context ctx);
	} igt_coherency_mode[] = {
	{ "cpu", cpu_set, cpu_get, always_valid },
	{ "gtt", gtt_set, gtt_get, needs_fence_registers },
	{ "wc", wc_set, wc_get, always_valid },
	{ "gpu", gpu_set, NULL, needs_mi_store_dword },
	{ },
	};

	static struct intel_engine_cs *
	random_engine(struct drm_i915_private i915, struct rnd_state prng)
	{
	struct intel_engine_cs *engine;
	unsigned int count;

	count = 0;
	for_each_uabi_engine(engine, i915)
	count++;

	count = i915_prandom_u32_max_state(count, prng);
	for_each_uabi_engine(engine, i915)
	if (count-- == 0)
	return engine;

	return NULL;
	}

	static int igt_gem_coherency(void *arg)
	{
	const unsigned int ncachelines = PAGE_SIZE/64;
	struct drm_i915_private *i915 = arg;
	const struct igt_coherency_mode read, write, *over;
	unsigned long count, n;
	u32 offsets, values;
	I915_RND_STATE(prng);
	struct context ctx;
	int err = 0;

	/*
	* We repeatedly write, overwrite and read from a sequence of
	* cachelines in order to try and detect incoherency (unflushed writes
	* from either the CPU or GPU). Each setter/getter uses our cache
	* domain API which should prevent incoherency.
	*/

	offsets = kmalloc_array(ncachelines, 2*sizeof(u32), GFP_KERNEL);
	if (!offsets)
	return -ENOMEM;
	for (count = 0; count < ncachelines; count++)
	offsets[count] = count * 64 + 4 * (count % 16);

	values = offsets + ncachelines;

	ctx.engine = random_engine(i915, &prng);
	if (!ctx.engine) {
	err = -ENODEV;
	goto out_free;
	}
	pr_info("%s: using %s\n", __func__, ctx.engine->name);
	intel_engine_pm_get(ctx.engine);

	for (over = igt_coherency_mode; over->name; over++) {
	if (!over->set)
	continue;

	if (!over->valid(&ctx))
	continue;

	for (write = igt_coherency_mode; write->name; write++) {
	if (!write->set)
	continue;

	if (!write->valid(&ctx))
	continue;

	for (read = igt_coherency_mode; read->name; read++) {
	if (!read->get)
	continue;

	if (!read->valid(&ctx))
	continue;

	for_each_prime_number_from(count, 1, ncachelines) {
	ctx.obj = i915_gem_object_create_internal(i915, PAGE_SIZE);
	if (IS_ERR(ctx.obj)) {
	err = PTR_ERR(ctx.obj);
	goto out_pm;
	}

	i915_random_reorder(offsets, ncachelines, &prng);
	for (n = 0; n < count; n++)
	values[n] = prandom_u32_state(&prng);

	for (n = 0; n < count; n++) {
	err = over->set(&ctx, offsets[n], ~values[n]);
	if (err) {
	pr_err("Failed to set stale value[%ld/%ld] in object using %s, err=%d\n",
	n, count, over->name, err);
	goto put_object;
	}
	}

	for (n = 0; n < count; n++) {
	err = write->set(&ctx, offsets[n], values[n]);
	if (err) {
	pr_err("Failed to set value[%ld/%ld] in object using %s, err=%d\n",
	n, count, write->name, err);
	goto put_object;
	}
	}

	for (n = 0; n < count; n++) {
	u32 found;

	err = read->get(&ctx, offsets[n], &found);
	if (err) {
	pr_err("Failed to get value[%ld/%ld] in object using %s, err=%d\n",
	n, count, read->name, err);
	goto put_object;
	}

	if (found != values[n]) {
	pr_err("Value[%ld/%ld] mismatch, (overwrite with %s) wrote [%s] %x read [%s] %x (inverse %x), at offset %x\n",
	n, count, over->name,
	write->name, values[n],
	read->name, found,
	~values[n], offsets[n]);
	err = -EINVAL;
	goto put_object;
	}
	}

	i915_gem_object_put(ctx.obj);
	}
	}
	}
	}
	out_pm:
	intel_engine_pm_put(ctx.engine);
	out_free:
	kfree(offsets);
	return err;

	put_object:
	i915_gem_object_put(ctx.obj);
	goto out_pm;
	}

	int i915_gem_coherency_live_selftests(struct drm_i915_private *i915)
	{
	static const struct i915_subtest tests[] = {
	SUBTEST(igt_gem_coherency),
	};

	return i915_live_subtests(tests, i915);
	}