drm/i915: Don't back up pinned LMEM context images and rings during suspend

Pinned context images are now reset during resume. Don't back them up,
and assuming that rings can be assumed empty at suspend, don't back them
up either.

Introduce a new object flag, I915_BO_ALLOC_PM_VOLATILE meaning that an
object is allowed to lose its content on suspend.

v3:
- Slight documentation clarification (Matthew Auld)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210922062527.865433-7-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -288,16 +288,19 @@ struct drm_i915_gem_object {
 	I915_SELFTEST_DECLARE(struct list_head st_link);
 
 	unsigned long flags;
-#define I915_BO_ALLOC_CONTIGUOUS BIT(0)
-#define I915_BO_ALLOC_VOLATILE   BIT(1)
-#define I915_BO_ALLOC_CPU_CLEAR  BIT(2)
-#define I915_BO_ALLOC_USER       BIT(3)
+#define I915_BO_ALLOC_CONTIGUOUS  BIT(0)
+#define I915_BO_ALLOC_VOLATILE    BIT(1)
+#define I915_BO_ALLOC_CPU_CLEAR   BIT(2)
+#define I915_BO_ALLOC_USER        BIT(3)
+/* Object is allowed to lose its contents on suspend / resume, even if pinned */
+#define I915_BO_ALLOC_PM_VOLATILE BIT(4)
 #define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
 			     I915_BO_ALLOC_VOLATILE | \
 			     I915_BO_ALLOC_CPU_CLEAR | \
-			     I915_BO_ALLOC_USER)
-#define I915_BO_READONLY         BIT(4)
-#define I915_TILING_QUIRK_BIT    5 /* unknown swizzling; do not release! */
+			     I915_BO_ALLOC_USER | \
+			     I915_BO_ALLOC_PM_VOLATILE)
+#define I915_BO_READONLY          BIT(5)
+#define I915_TILING_QUIRK_BIT     6 /* unknown swizzling; do not release! */
 
 	/**
 	 * @mem_flags - Mutable placement-related flags

drivers/gpu/drm/i915/gem/i915_gem_ttm_pm.c

@@ -60,6 +60,9 @@ static int i915_ttm_backup(struct i915_gem_apply_to_region *apply,
 	if (!pm_apply->backup_pinned)
 		return 0;
 
+	if (obj->flags & I915_BO_ALLOC_PM_VOLATILE)
+		return 0;
+
 	backup = i915_gem_object_create_shmem(i915, obj->base.size);
 	if (IS_ERR(backup))
 		return PTR_ERR(backup);

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -942,7 +942,8 @@ __lrc_alloc_state(struct intel_context *ce, struct intel_engine_cs *engine)
 		context_size += PAGE_SIZE;
 	}
 
-	obj = i915_gem_object_create_lmem(engine->i915, context_size, 0);
+	obj = i915_gem_object_create_lmem(engine->i915, context_size,
+					  I915_BO_ALLOC_PM_VOLATILE);
 	if (IS_ERR(obj))
 		obj = i915_gem_object_create_shmem(engine->i915, context_size);
 	if (IS_ERR(obj))

drivers/gpu/drm/i915/gt/intel_ring.c

@@ -112,7 +112,8 @@ static struct i915_vma *create_ring_vma(struct i915_ggtt *ggtt, int size)
 	struct drm_i915_gem_object *obj;
 	struct i915_vma *vma;
 
-	obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE);
+	obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE |
+					  I915_BO_ALLOC_PM_VOLATILE);
 	if (IS_ERR(obj) && i915_ggtt_has_aperture(ggtt))
 		obj = i915_gem_object_create_stolen(i915, size);
 	if (IS_ERR(obj))