From a50794f26f52c66cb793d5d392f5f19bc2962cdd Mon Sep 17 00:00:00 2001 From: Ramalingam C Date: Mon, 2 May 2022 19:45:08 +0530 Subject: [PATCH] uapi/drm/i915: Document memory residency and Flat-CCS capability of obj Capture the impact of memory region preference list of the objects, on their memory residency and Flat-CCS capability. v2: Fix the Flat-CCS capability of an obj with {lmem, smem} preference list [Thomas] v3: Reworded the doc [Matt] v4: Fixed Typos and spelling mistakes [Tvrtko, Joonas] Signed-off-by: Ramalingam C cc: Matthew Auld cc: Thomas Hellstrom cc: Daniel Vetter cc: Jon Bloomfield cc: Lionel Landwerlin cc: Kenneth Graunke cc: mesa-dev@lists.freedesktop.org cc: Jordan Justen cc: Tony Ye Reviewed-by: Matthew Auld Acked-by: Jordan Justen Link: https://patchwork.freedesktop.org/patch/msgid/20220502141508.2327-1-ramalingam.c@intel.com --- include/uapi/drm/i915_drm.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h index a2def7b270097..de49b68b4fc87 100644 --- a/include/uapi/drm/i915_drm.h +++ b/include/uapi/drm/i915_drm.h @@ -3443,6 +3443,22 @@ 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. + * + * Note that userspace has no means of knowing the current backing region + * for objects where @num_regions is larger than one. The kernel will only + * ensure that the priority order of the @regions array is honoured, either + * when initially placing the object, or when moving memory around due to + * memory pressure + * + * On Flat-CCS capable HW, compression is supported for the objects residing + * in I915_MEMORY_CLASS_DEVICE. When such objects (compressed) have other + * memory class in @regions and migrated (by i915, due to memory + * constraints) to the non I915_MEMORY_CLASS_DEVICE region, then i915 needs to + * decompress the content. But i915 doesn't have the required information to + * decompress the userspace compressed objects. + * + * So i915 supports Flat-CCS, on the objects which can reside only on + * I915_MEMORY_CLASS_DEVICE regions. */ struct drm_i915_gem_create_ext_memory_regions { /** @base: Extension link. See struct i915_user_extension. */ -- 2.30.2