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

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Date:   Tue, 1 Sep 2020 15:26:56 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Simon Ser <contact@...rsion.fr>
Cc:     Ville Syrjälä 
        <ville.syrjala@...ux.intel.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>,
        Sidong Yang <realwakka@...il.com>
Subject: Re: [PATCH] drm/vkms: add support for gamma_set interface

On Tue, Sep 01, 2020 at 08:57:37AM +0000, Simon Ser wrote:
> 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

Hm not sure what 8bpc format you mean here, because we have C8 (needs
gamma table or doesn't work) and the 8b greyscale one with the R8 one. If
you ask for legacy 8bpc you get C8.

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

Yeah the test should skip if gamma isn't there.
-Daniel

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

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