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drm: drm_fourcc: Add generic alias for 16_16_TILE modifier

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In cases such as DRM_FORMAT_MOD_SAMSUNG_16_16_TILE, the modifier
describes a generic pixel re-ordering which can be applicable to
multiple vendors.

Define an alias: DRM_FORMAT_MOD_GENERIC_16_16_TILE, which can be
used to describe this layout in a vendor-neutral way, and add a
comment about the expected usage of such "generic" modifiers.

Changes in v2:
 - Move note about future cases to comment (Daniel)

Signed-off-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200626164800.11595-1-brian.starkey@arm.com
This commit is contained in:
Brian Starkey 2020-06-26 17:48:00 +01:00 committed by Liviu Dudau
parent be8c8403f6
commit 9ac2b63791
1 changed files with 25 additions and 0 deletions
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25
include/uapi/drm/drm_fourcc.h
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@ -346,8 +346,33 @@ extern "C" {
* When adding a new token please document the layout with a code comment,
* similar to the fourcc codes above. drm_fourcc.h is considered the
* authoritative source for all of these.
*
* Generic modifier names:
*
* DRM_FORMAT_MOD_GENERIC_* definitions are used to provide vendor-neutral names
* for layouts which are common across multiple vendors. To preserve
* compatibility, in cases where a vendor-specific definition already exists and
* a generic name for it is desired, the common name is a purely symbolic alias
* and must use the same numerical value as the original definition.
*
* Note that generic names should only be used for modifiers which describe
* generic layouts (such as pixel re-ordering), which may have
* independently-developed support across multiple vendors.
*
* In future cases where a generic layout is identified before merging with a
* vendor-specific modifier, a new 'GENERIC' vendor or modifier using vendor
* 'NONE' could be considered. This should only be for obvious, exceptional
* cases to avoid polluting the 'GENERIC' namespace with modifiers which only
* apply to a single vendor.
*
* Generic names should not be used for cases where multiple hardware vendors
* have implementations of the same standardised compression scheme (such as
* AFBC). In those cases, all implementations should use the same format
* modifier(s), reflecting the vendor of the standard.
*/
#define DRM_FORMAT_MOD_GENERIC_16_16_TILE DRM_FORMAT_MOD_SAMSUNG_16_16_TILE
/*
* Invalid Modifier
*