[PATCH v2 1/2] drm/blend: Add per-plane pixel blend mode property

[Lowry Li]

On Thu, May 31, 2018 at 03:51:37PM +0100, Emil Velikov wrote:
> Hi Lowry,
> 
> Small drive-by suggestion. Haven't checked if others have pointed it
> out previously :-\
> 
> On 30 May 2018 at 12:23, Lowry Li <lowry.li at arm.com> wrote:
> 
> > +/**
> > + * drm_plane_create_blend_mode_property - create a new blend mode property
> > + * @plane: drm plane
> > + * @supported_modes: bitmask of supported modes, must include
> > + *                  BIT(DRM_MODE_BLEND_PREMULTI)
> > + *
> There are two possible blend modes (ignoring 'none'), yet premult must
> be supported.
> What if the hardware can do only "coverage"?
> 
> One-liner explaining why things are as-is would be a great move.
> 
> HTH
> Emil
Hi Emil,

Thanks for your comments. Yes, we'd add explaining on the comments of
the function.
About why and regarding supporting more than pre-mult, because the
current DRM assumption is that alpha is premultiplied, and old
userspace can break if the property defaults to coverage.
Please also refer to the discuss record as below on IRC.
https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&highlight_names=&date=2018-04-25&show_html=true
Please read from around 12:45 to 12:49. :)

-- 
Regards,
Lowry