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

[Simon Ser]

On Tuesday, September 1, 2020 3:26 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:

> 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@xxxxxxxxxxxxxxx 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.

Why do we need a gamma LUT for C8 and R8? There shouldn't be any
precision loss, right?

> > -   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