drm/i915: use consistent CPU mappings for pin_map users

For discrete, users of pin_map() needs to obey the same rules at the TTM
backend, where we map system only objects as WB, and everything else as
WC. The simplest for now is to just force the correct mapping type as
per the new rules for discrete.

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210705135310.1502437-1-matthew.auld@intel.com

1 files changed, 29 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
index f2f850e31b8e..0c9d28423d45 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
@@ -321,8 +321,7 @@ static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj,
 	dma_addr_t addr;
 	void *vaddr;
 
-	if (type != I915_MAP_WC)
-		return ERR_PTR(-ENODEV);
+	GEM_BUG_ON(type != I915_MAP_WC);
 
 	if (n_pfn > ARRAY_SIZE(stack)) {
 		/* Too big for stack -- allocate temporary array instead */
@@ -374,6 +373,34 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
 	}
 	GEM_BUG_ON(!i915_gem_object_has_pages(obj));
 
+	/*
+	 * For discrete our CPU mappings needs to be consistent in order to
+	 * function correctly on !x86. When mapping things through TTM, we use
+	 * the same rules to determine the caching type.
+	 *
+	 * The caching rules, starting from DG1:
+	 *
+	 *	- If the object can be placed in device local-memory, then the
+	 *	  pages should be allocated and mapped as write-combined only.
+	 *
+	 *	- Everything else is always allocated and mapped as write-back,
+	 *	  with the guarantee that everything is also coherent with the
+	 *	  GPU.
+	 *
+	 * Internal users of lmem are already expected to get this right, so no
+	 * fudging needed there.
+	 */
+	if (i915_gem_object_placement_possible(obj, INTEL_MEMORY_LOCAL)) {
+		if (type != I915_MAP_WC && !obj->mm.n_placements) {
+			ptr = ERR_PTR(-ENODEV);
+			goto err_unpin;
+		}
+
+		type = I915_MAP_WC;
+	} else if (IS_DGFX(to_i915(obj->base.dev))) {
+		type = I915_MAP_WB;
+	}
+
 	ptr = page_unpack_bits(obj->mm.mapping, &has_type);
 	if (ptr && has_type != type) {
 		if (pinned) {