[PATCH v2] uapi/drm/drm_fourcc.h: Note on platform specificity for format modifiers

[Daniel Vetter]

On Fri, May 08, 2020 at 08:56:28AM +0200, Daniel Vetter wrote:
> On Wed, May 06, 2020 at 03:08:27PM +0300, Mika Kahola wrote:
> > Make an additional note on DRM format modifiers for x and y tiling. These
> > format modifiers are defined for BDW+ platforms and therefore definition
> > is not valid for older gens. This is due to address swizzling for tiled
> > surfaces is no longer used. For newer platforms main memory controller has
> > a more effective address swizzling algorithm.
> > 
> > v2: Rephrase comment (Daniel)
> > 
> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Ok I assumed you'd just push that to drm-intel with commit rights or
something, but that got stuck so applying to drm-misc-next now.

Cheers, Daniel
> 
> > ---
> >  include/uapi/drm/drm_fourcc.h | 18 ++++++++++++------
> >  1 file changed, 12 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 8bc0b31597d8..9e488d10f8b4 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -354,9 +354,12 @@ extern "C" {
> >   * a platform-dependent stride. On top of that the memory can apply
> >   * platform-depending swizzling of some higher address bits into bit6.
> >   *
> > - * This format is highly platforms specific and not useful for cross-driver
> > - * sharing. It exists since on a given platform it does uniquely identify the
> > - * layout in a simple way for i915-specific userspace.
> > + * Note that this layout is only accurate on intel gen 8+ or valleyview chipsets.
> > + * On earlier platforms the is highly platforms specific and not useful for
> > + * cross-driver sharing. It exists since on a given platform it does uniquely
> > + * identify the layout in a simple way for i915-specific userspace, which
> > + * facilitated conversion of userspace to modifiers. Additionally the exact
> > + * format on some really old platforms is not known.
> >   */
> >  #define I915_FORMAT_MOD_X_TILED	fourcc_mod_code(INTEL, 1)
> >  
> > @@ -369,9 +372,12 @@ extern "C" {
> >   * memory can apply platform-depending swizzling of some higher address bits
> >   * into bit6.
> >   *
> > - * This format is highly platforms specific and not useful for cross-driver
> > - * sharing. It exists since on a given platform it does uniquely identify the
> > - * layout in a simple way for i915-specific userspace.
> > + * Note that this layout is only accurate on intel gen 8+ or valleyview chipsets.
> > + * On earlier platforms the is highly platforms specific and not useful for
> > + * cross-driver sharing. It exists since on a given platform it does uniquely
> > + * identify the layout in a simple way for i915-specific userspace, which
> > + * facilitated conversion of userspace to modifiers. Additionally the exact
> > + * format on some really old platforms is not known.
> >   */
> >  #define I915_FORMAT_MOD_Y_TILED	fourcc_mod_code(INTEL, 2)
> >  
> > -- 
> > 2.20.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch