Re: [v3 6/7] drm: Add Client Cap for advance gamma mode

Daniel Vetter
2019-04-15T19:20:55Z

On Mon, Apr 15, 2019 at 4:14 PM Lankhorst, Maarten
<maarten.lankhorst@intel.com> wrote:
>
> mån 2019-04-15 klockan 19:26 +0530 skrev Sharma, Shashank:
> > > -----Original Message-----
> > > From: Lankhorst, Maarten
> > > Sent: Monday, April 15, 2019 4:28 PM
> > > To: Shankar, Uma <uma.shankar@intel.com>; intel-gfx@lists.freedeskt
> > > op.org; dri-
> > > devel@lists.freedesktop.org
> > > Cc: Syrjala, Ville <ville.syrjala@intel.com>; emil.l.velikov@gmail.
> > > com;
> > > sam@ravnborg.org; Roper, Matthew D <matthew.d.roper@intel.com>;
> > > seanpaul@chromium.org; brian.starkey@arm.com; dcastagna@chromium.or
> > > g;
> > > Sharma, Shashank <shashank.sharma@intel.com>
> > > Subject: Re: [v3 6/7] drm: Add Client Cap for advance gamma mode
> > >
> > > fre 2019-04-12 klockan 15:51 +0530 skrev Uma Shankar:
> > > > Introduced a client cap for advance cap mode
> > > > capability. Userspace should set this to get
> > > > to be able to use the new gamma_mode property.
> > > >
> > > > If this is not set, driver will work in legacy
> > > > mode.
> > > >
> > > > Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> > >
> > > Nack, this doesn't seem like a sensible idea. We already guard it
> > > behind the gamma mode property. Userspace shouldn't set the gamma
> > > mode
> > > to a value it doesn't understand.
> > >
> > > ~Maarten
> >
> > Hey Maarten,
> > In that case, what do you suggest should be the right way to do this
> > ?
> >
> > @Ville, any comments here ?
> >
> I would say drop this patch, and just enable segmented gamma
> unconditionally, it's not the first property that can cause trouble
> when not understood.

Yeah, thus far we went with "new properties should have the old
behaviour as default, no cap/flag needed". If you mix old&new
userspace and stuff starts looking funny, that's not a regression imo.
Also, it's a very uncommon use-case.

Wrt reset to default: fbdev emulation should do that for anything
that's too fancy, which is generally enough for the "developer of
compositors" use case. That part might be missing in the gamma/ctm
support in general I think.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch