drm/i915/ttm: Add I915_BO_PREALLOC

Add a mechanism to preserve existing data when creating
a TTM object with the I915_BO_ALLOC_USER flag. This will
be used in the subsequent patch where the I915_BO_ALLOC_USER
flag will be applied to the framebuffer object. For a pre-allocated
framebuffer without the I915_BO_PREALLOC flag.

TTM would clear the content, which is not desirable.
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230404143100.10452-1-nirmoy.das@intel.com

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

@@ -328,6 +328,12 @@ struct drm_i915_gem_object {
  */
 #define I915_BO_ALLOC_GPU_ONLY	  BIT(6)
 #define I915_BO_ALLOC_CCS_AUX	  BIT(7)
+/*
+ * Object is allowed to retain its initial data and will not be cleared on first
+ * access if used along with I915_BO_ALLOC_USER. This is mainly to keep
+ * preallocated framebuffer data intact while transitioning it to i915drmfb.
+ */
+#define I915_BO_PREALLOC	  BIT(8)
 #define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
 			     I915_BO_ALLOC_VOLATILE | \
 			     I915_BO_ALLOC_CPU_CLEAR | \
@@ -335,10 +341,11 @@ struct drm_i915_gem_object {
 			     I915_BO_ALLOC_PM_VOLATILE | \
 			     I915_BO_ALLOC_PM_EARLY | \
 			     I915_BO_ALLOC_GPU_ONLY | \
-			     I915_BO_ALLOC_CCS_AUX)
-#define I915_BO_READONLY          BIT(8)
-#define I915_TILING_QUIRK_BIT     9 /* unknown swizzling; do not release! */
-#define I915_BO_PROTECTED         BIT(10)
+			     I915_BO_ALLOC_CCS_AUX | \
+			     I915_BO_PREALLOC)
+#define I915_BO_READONLY          BIT(9)
+#define I915_TILING_QUIRK_BIT     10 /* unknown swizzling; do not release! */
+#define I915_BO_PROTECTED         BIT(11)
 	/**
 	 * @mem_flags - Mutable placement-related flags
 	 *

drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c

@@ -560,7 +560,7 @@ int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
 	struct dma_fence *migration_fence = NULL;
 	struct ttm_tt *ttm = bo->ttm;
 	struct i915_refct_sgt *dst_rsgt;
-	bool clear;
+	bool clear, prealloc_bo;
 	int ret;
 
 	if (GEM_WARN_ON(i915_ttm_is_ghost_object(bo))) {
@@ -590,7 +590,8 @@ int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
 		return PTR_ERR(dst_rsgt);
 
 	clear = !i915_ttm_cpu_maps_iomem(bo->resource) && (!ttm || !ttm_tt_is_populated(ttm));
-	if (!(clear && ttm && !(ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC))) {
+	prealloc_bo = obj->flags & I915_BO_PREALLOC;
+	if (!(clear && ttm && !((ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) && !prealloc_bo))) {
 		struct i915_deps deps;
 
 		i915_deps_init(&deps, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);