[PATCH v2] drm: drm_fourcc: Add generic alias for 16_16_TILE modifier

[Brian Starkey]

On Mon, Jun 29, 2020 at 10:32:41AM +0200, Daniel Vetter wrote:
> On Fri, Jun 26, 2020 at 05:48:00PM +0100, Brian Starkey wrote:
> > 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 at arm.com>
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Thanks. I guess this should go into drm-misc-next? @Liviu would you be
able to pick it up?

Cheers,
-Brian

> 
> > ---
> >  include/uapi/drm/drm_fourcc.h | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> > 
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 299f9ac4840b..cb3db4a21012 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -345,8 +345,33 @@ 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
> >   *
> > -- 
> > 2.17.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch