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

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -625,6 +625,40 @@ int i915_gem_object_migrate(struct drm_i915_gem_object *obj,
 	return obj->ops->migrate(obj, mr);
 }
 
+/**
+ * i915_gem_object_placement_possible - Check whether the object can be
+ * placed at certain memory type
+ * @obj: Pointer to the object
+ * @type: The memory type to check
+ *
+ * Return: True if the object can be placed in @type. False otherwise.
+ */
+bool i915_gem_object_placement_possible(struct drm_i915_gem_object *obj,
+					enum intel_memory_type type)
+{
+	unsigned int i;
+
+	if (!obj->mm.n_placements) {
+		switch (type) {
+		case INTEL_MEMORY_LOCAL:
+			return i915_gem_object_has_iomem(obj);
+		case INTEL_MEMORY_SYSTEM:
+			return i915_gem_object_has_pages(obj);
+		default:
+			/* Ignore stolen for now */
+			GEM_BUG_ON(1);
+			return false;
+		}
+	}
+
+	for (i = 0; i < obj->mm.n_placements; i++) {
+		if (obj->mm.placements[i]->type == type)
+			return true;
+	}
+
+	return false;
+}
+
 void i915_gem_init__objects(struct drm_i915_private *i915)
 {
 	INIT_WORK(&i915->mm.free_work, __i915_gem_free_work);

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -12,6 +12,7 @@
 #include <drm/drm_device.h>
 
 #include "display/intel_frontbuffer.h"
+#include "intel_memory_region.h"
 #include "i915_gem_object_types.h"
 #include "i915_gem_gtt.h"
 #include "i915_gem_ww.h"
@@ -607,6 +608,9 @@ bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,
 int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,
 				   unsigned int flags);
 
+bool i915_gem_object_placement_possible(struct drm_i915_gem_object *obj,
+					enum intel_memory_type type);
+
 #ifdef CONFIG_MMU_NOTIFIER
 static inline bool
 i915_gem_object_is_userptr(struct drm_i915_gem_object *obj)

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) {