[PATCH 4/4] uapi/drm/i915: Update the placement list impact on obj residency

[Hellstrom, Thomas]

On Thu, 2022-04-21 at 17:08 +0530, Ramalingam C wrote:
> Object created with list of memory classes as placement preferences,
> can
> be backed with any memory class of the list as per kernel's migration
> policy for the memory contrain situation. Userspace won't be notified
> of
> the memory residency change at this scenario.
> 
> And also Flat-CCS compression is supported only on objects of
> I915_MEMORY_CLASS_DEVICE. When the Flat-CCS compressed objects
> migrates
> out of I915_MEMORY_CLASS_DEVICE, due to memory constrain, content
> will
> be decompressed without notifying the userpsace.

userspace
> 

> Record these details in Kernel documentation.
> 
> Signed-off-by: Ramalingam C <ramalingam.c at intel.com>
> ---
>  include/uapi/drm/i915_drm.h | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/include/uapi/drm/i915_drm.h
> b/include/uapi/drm/i915_drm.h
> index 35ca528803fd..8b25dd6a157a 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -3393,6 +3393,20 @@ struct drm_i915_gem_create_ext {
>   * At which point we get the object handle in
> &drm_i915_gem_create_ext.handle,
>   * along with the final object size in
> &drm_i915_gem_create_ext.size, which
>   * should account for any rounding up, if required.
> + *
> + * If an object is created with list of memory classes as their
> placement
> + * preference, kernel could use one of the memory class as the
> backing storage
> + * based on the memory availability. At memory pressure kernel could
> migrate the
> + * objects content from one memory class to another, given in the
> placement list.
> + *
> + * With placement preference list, userpace can't be sure about the
> object's memory
> + * residence.
> + *
> + * Flat-CCS compression is supported only for objects of
> I915_MEMORY_CLASS_DEVICE.
> + * If the object has other placement preferences, and if the content
> is
> + * migrated (by kernel due to memory constrain) to a memory class
> which is other
> + * than I915_MEMORY_CLASS_DEVICE, object content will be
> decompressed by kernel.
> + * Userpace will be ignorant of this Flat-CCS state change.

Same question here as for previous commit.



>   */
>  struct drm_i915_gem_create_ext_memory_regions {
>         /** @base: Extension link. See struct i915_user_extension. */