linux-kernel - Re: [PATCH] drm/vkms: add support for gamma

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Date:   Tue, 01 Sep 2020 08:57:37 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Sidong Yang <realwakka@...il.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Emil Velikov <emil.l.velikov@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Melissa Wen <melissa.srw@...il.com>
Subject: Re: [PATCH] drm/vkms: add support for gamma_set interface

On Monday, August 31, 2020 3:48 PM, Ville Syrjälä <ville.syrjala@...ux.intel.com> wrote:

> > > It doesn't seem like this IGT test's goal is to exercise support for
> > > gamma LUTs. Does the test just tries to reset the gamma LUT to linear?
> > > If so, I think the IGT test should be fixed to ignore "I don't support
> > > gamma" errors.
> >
> > It seems like that IGT test pixel-format is to make gamma lut like below.
> > for (i = 0; i < lut_size; i++)
> > lut[i] = (i * 0xffff / (lut_size - 1)) & mask;
> > And set this table to drm driver. and test begins. It's the test about pixel
> > format. I think you're right. It's not about gamma lut.
>
> The point of the gamma LUT stuff in the pixel format test is to throw
> away a bunch of the lsbs so that the test passes when the result is
> "close enough" to the 8bpc RGB reference image. Without it we would
> never get a crc match when testing non-8bpc or YCbCr formats.

OK, that makes sense. Would it be sensible to:

- Don't set gamma if the pixel format being tested is 8bpc
- Make the test skip if the pixel format is >8bpc and gamma isn't
  supported