On 2021-07-05 at 14:53:07 +0100, Matthew Auld wrote:
> 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>
LGTM.
Reviewed-by: Ramalingam C <ramalingam.c@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
>
