[PATCH] drm/amdgpu/dc: Pixel encoding DRM property and module parameter

[Alex Deucher]

On Mon, Sep 28, 2020 at 4:24 PM James Ettle <james at ettle.org.uk> wrote:
>
> On Mon, 2020-09-28 at 16:12 -0400, Kazlauskas, Nicholas wrote:
> >
> > The problem with the module parameters is that it'd be applying a
> > default to every DRM connector. No way to specify different defaults
> > per
> > DRM connector, nor do we know the full connector set at driver
> > initialization. The list is dynamic and can change when you
> > plug/unplug
> > MST displays.
>
> I just want to point out that the module parameter does support
> connector-specific values, e.g.
>
>   amdgpu.pixel_encoding=HDMI-A-1:rgb
>
> should only affect the connector named HDMI-A-1 (unless I've coded it
> wrong -- I don't have enough video ports to test it thoroughly). If
> there's no such-named connector the parameter should be ignored. In
> contrast with no named connector given, e.g.
>
>   amdgpu.pixel_encoding=rgb
>
> should match any connector. Multiple connectors can be given comma-
> separated. I admit the solution here is crude -- it just stores the
> string and rescans it when required.

Yes, but module parameters global for all devices claimed by that
driver.  E.g., if you have a system with 2 or 3 AMD GPUs in it, that
will be applied to all of them.  I think if we want to be able to set
KMS properties on the kernel command line, we should add the
functionality to the drm core so it works for all drivers and
properties.  We already have this for basic modesetting.

Alex