Convert all the drm_i915_gem_caching bits to proper kernel doc.
Suggested-by: Daniel Vetter <daniel@xxxxxxxx>
Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Jordan Justen <jordan.l.justen@xxxxxxxxx>
Cc: Kenneth Graunke <kenneth@xxxxxxxxxxxxx>
Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Ramalingam C <ramalingam.c@xxxxxxxxx>
---
include/uapi/drm/i915_drm.h | 70 +++++++++++++++++++++++--------------
1 file changed, 43 insertions(+), 27 deletions(-)
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 2f70c48567c0..d13c6c5fad04 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1363,43 +1363,59 @@ struct drm_i915_gem_busy {
};
/**
- * I915_CACHING_NONE
+ * struct drm_i915_gem_caching - Set or get the caching for given object
+ * handle.
*
- * GPU access is not coherent with cpu caches. Default for machines without an
- * LLC.
- */
-#define I915_CACHING_NONE 0
-/**
- * I915_CACHING_CACHED
+ * Allow userspace to control the GTT caching bits for a given object when the
+ * object is later mapped through the ppGTT(or GGTT on older platforms lacking
+ * ppGTT support, or if the object is used for scanout). Note that this might
+ * require unbinding the object from the GTT first, if its current caching value
+ * doesn't match.
*
- * GPU access is coherent with cpu caches and furthermore the data is cached in
- * last-level caches shared between cpu cores and the gpu GT. Default on
- * machines with HAS_LLC.
- */
-#define I915_CACHING_CACHED 1
-/**
- * I915_CACHING_DISPLAY
*
- * Special GPU caching mode which is coherent with the scanout engines.
- * Transparently falls back to I915_CACHING_NONE on platforms where no special
- * cache mode (like write-through or gfdt flushing) is available. The kernel
- * automatically sets this mode when using a buffer as a scanout target.
- * Userspace can manually set this mode to avoid a costly stall and clflush in
- * the hotpath of drawing the first frame.
*/
-#define I915_CACHING_DISPLAY 2
-
struct drm_i915_gem_caching {
/**
- * Handle of the buffer to set/get the caching level of. */
+ * @handle: Handle of the buffer to set/get the caching level.
+ */
__u32 handle;
/**
- * Cacheing level to apply or return value
+ * @caching: The GTT caching level to apply or possible return value.
+ *
+ * The supported @caching values:
*
- * bits0-15 are for generic caching control (i.e. the above defined
- * values). bits16-31 are reserved for platform-specific variations
- * (e.g. l3$ caching on gen7). */
+ * I915_CACHING_NONE:
+ *
+ * GPU access is not coherent with CPU caches. Default for machines
+ * without an LLC. This means we need to manually clflush, if we want
+ * GPU access to be coherent.
+ *
+ * I915_CACHING_CACHED:
+ *
+ * GPU access is coherent with CPU caches and furthermore the data is
+ * cached in last-level caches shared between CPU cores and the GPU GT.
+ * Default on machines with HAS_LLC. In general the fast shared
+ * last-level cache(HAS_LLC) is considered much faster then platforms
+ * which only support snooping(HAS_SNOOP), hence by default
+ *
+ * I915_CACHING_DISPLAY:
+ *
+ * Special GPU caching mode which is coherent with the scanout engines.
+ * Transparently falls back to I915_CACHING_NONE on platforms where no
+ * special cache mode (like write-through or gfdt flushing) is
+ * available. The kernel automatically sets this mode when using a
+ * buffer as a scanout target. Userspace can manually set this mode to
+ * avoid a costly stall and clflush in the hotpath of drawing the first
+ * frame.
+ *
+ * Side note: On gen8+ this no longer does much since we lost the GGTT
+ * caching bits. Although setting this is harmless, since it still
+ * effectively falls back to I915_CACHING_NONE.
+ */
+#define I915_CACHING_NONE 0
+#define I915_CACHING_CACHED 1
+#define I915_CACHING_DISPLAY 2
__u32 caching;
};
--
2.26.3
