Re: [PATCH] drm/vc4: Ignore alpha on primary plane

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Mar 02, 2018 at 04:06:58PM +0100, Stefan Schake wrote:
> Hey Ville,
> 
> On Fri, Mar 2, 2018 at 3:43 PM, Ville Syrjälä
> <ville.syrjala@linux.intel.com> wrote:
> > On Fri, Mar 02, 2018 at 04:39:22PM +0200, Ville Syrjälä wrote:
> >> If you want the plane to always be opaque you shouldn't expose any
> >> formats with alpha.
> >>
> >> Also what happens if one disables the primary plane? Or does the driver
> >> not allow that?
> >
> > Or just makes the plane not cover the entire screen?
> 
> We've exposed alpha formats in the past so disabling that now would break
> userspace, certainly Android that chooses alpha-everything.

So it refuses to even run on hardware that can't do per-pixel alpha on
the primary plane?

> The VC4 HVS
> has no fixed planes so I'll acknowledge that the concept of a primary plane
> is somewhat dubious and userspace could disable it or make it not cover the
> entire screen, making this ineffective.
> 
> But then ultimately there doesn't seem to be a standard for what the display
> is supposed to be if you have transparent pixels with no plane to blend to
> below.

The standard is black. IMO it's a driver bug if it fails to do that.

> This helps in the common case, the belts&braces fix would be to
> enable the VC4 HVS background color fill incurring a fixed overhead that
> in most cases is wasted because the composition ends up being opaque.
> 
> Thanks,
> Stefan

-- 
Ville Syrjälä
Intel OTC
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