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758941ab0c
The BROADCOM_SAND128 modifier is usually used with an extra parameter to pass in the stride via a side channel. Quoting from drm_fourcc.h: > The pitch between the start of each column is set to optimally > switch between SDRAM banks. This is passed as the number of lines > of column width in the modifier (we can't use the stride value due > to various core checks that look at it , so you should set the > stride to width*cpp). So apparently this is just a workaround for limitations in some kernel APIs. DRM modifiers, however, are arguably a bad fit for extra parameters that aren't known in advance. In the Wayland/KMS ecosystem many components depend on being able to treat modifiers as opaque, e.g. for negotiations etc. In practice the current approach requires various software components to manually use the `DRM_FORMAT_MOD_BROADCOM_SAND128_COL_HEIGHT()` macro - using the `DRM_FORMAT_MOD_BROADCOM_SAND128` modifier directly with formats like `NV12` results in a rejection in the KMS driver and corrupted output in Mesa (because we'd bail out early in `v3d_sand8_blit()`). Fortunately the stride check limitations mentioned above don't seem to apply to Mesa though. Thus we can just add support for the base modifier and stride (coming from V4L2), allowing various toolkits, Wayland compositors and V4L2 decoder implementations to support e.g. `NV12` + `DRM_FORMAT_MOD_BROADCOM_SAND128` (`NC12` in V4L2) in a generic way. Notes: 1. Wayland compositors trying to offload composition to KMS will still fail when doing a test commit. 2. There is another limitation - in the V4L2 MPLANE API - that requires userspace to know the correct offset of the second plane. That's a known API limitation though and only affects V4L2 decoder implementations. Cc: mesa-stable Signed-off-by: Robert Mader <robert.mader@collabora.com> Reviewed-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32033> |
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