linux-kernel - Re: [PATCH v2 1/3] drm/panel-edp: add fat warning against adding new panel compatibles

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Date: Fri, 31 May 2024 02:11:09 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Doug Anderson <dianders@...omium.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-rockchip@...ts.infradead.org, 
	Jeffrey Hugo <quic_jhugo@...cinc.com>
Subject: Re: [PATCH v2 1/3] drm/panel-edp: add fat warning against adding new
 panel compatibles

On Thu, May 30, 2024 at 07:33:59AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Tue, May 28, 2024 at 4:52 PM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
> >
> > Add a fat warning against adding new panel compatibles to the panel-edp
> > driver. All new users of the eDP panels are supposed to use the generic
> > "edp-panel" compatible device on the AUX bus. The remaining compatibles
> > are either used by the existing DT or were used previously and are
> > retained for backwards compatibility.
> >
> > Suggested-by: Doug Anderson <dianders@...omium.org>
> > Reviewed-by: Neil Armstrong <neil.armstrong@...aro.org>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > ---
> >  drivers/gpu/drm/panel/panel-edp.c | 18 +++++++++++++++++-
> >  1 file changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-edp.c b/drivers/gpu/drm/panel/panel-edp.c
> > index 6db277efcbb7..95b25ec67168 100644
> > --- a/drivers/gpu/drm/panel/panel-edp.c
> > +++ b/drivers/gpu/drm/panel/panel-edp.c
> > @@ -1776,7 +1776,23 @@ static const struct of_device_id platform_of_match[] = {
> >         {
> >                 /* Must be first */
> >                 .compatible = "edp-panel",
> > -       }, {
> > +       },
> > +       /*
> > +        * Do not add panels to the list below unless they cannot be handled by
> > +        * the generic edp-panel compatible.
> > +        *
> > +        * The only two valid reasons are:
> > +        * - because of the panel issues (e.g. broken EDID or broken
> > +        *   identification),
> > +        * - because the platform which uses the panel didn't wire up the AUX
> > +        *   bus properly.
> > +        *
> > +        * In all other cases the platform should use the aux-bus and declare
> > +        * the panel using the 'edp-panel' compatible as a device on the AUX
> > +        * bus. The lack of the aux-bus support is not a valid case. Platforms
> > +        * are urged to be converted to declaring panels in a proper way.
> 
> I'm still at least slightly confused by the wording. What is "the lack
> of the aux-bus support". I guess this is different from the valid
> reason of "the platform which uses the panel didn't wire up the AUX
> bus properly" but I'm not sure how. Maybe you can explain?
> 
> I guess I'd write it like this:
> 
>     /*
>      * Do not add panels to the list below unless they cannot be handled by
>      * the generic edp-panel compatible.
>      *
>      * The only two valid reasons are:
>      * - because of the panel issues (e.g. broken EDID or broken
>      *   identification).
>      * - because the platform which uses the panel didn't wire up the AUX
>      *   bus properly. NOTE that, though this is a marginally valid reason,
>      *   some justification needs to be made for why the platform can't
>      *   wire up the AUX bus properly.
>      *
>      * In all other cases the platform should use the aux-bus and declare
>      * the panel using the 'edp-panel' compatible as a device on the AUX
>      * bus.
>      */
> 
> What do you think? In any case, it probably doesn't matter much. The
> important thing is some sort of warning here telling people not to add
> to the table. In that sense:

Ack, I'l update the wording in a similar way.

> 
> Reviewed-by: Douglas Anderson <dianders@...omium.org>

-- 
With best wishes
Dmitry