Re: [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46

[Maxime Ripard <maxime@cerno.tech>]

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On Thu, Jul 28, 2022 at 02:18:38PM -0700, Doug Anderson wrote:
> Hi,
> 
> On Thu, Jul 28, 2022 at 10:34 AM Abhinav Kumar
> <quic_abhinavk@quicinc.com> wrote:
> >
> > Hi Rob and Doug
> >
> > On 7/22/2022 10:36 AM, Rob Clark wrote:
> > > On Fri, Jul 22, 2022 at 9:48 AM Doug Anderson <dianders@chromium.org> wrote:
> > >>
> > >> Hi,
> > >>
> > >> On Fri, Jul 22, 2022 at 9:37 AM Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
> > >>>
> > >>> + sankeerth
> > >>>
> > >>> Hi Doug
> > >>>
> > >>> On 7/21/2022 3:23 PM, Douglas Anderson wrote:
> > >>>> The Sharp LQ140M1JW46 panel is on the Qualcomm sc7280 CRD reference
> > >>>> board. This panel supports 144 Hz and 60 Hz. In the EDID, the 144 Hz
> > >>>> mode is listed first and thus is marked preferred. The EDID decode I
> > >>>> ran says:
> > >>>>
> > >>>>     First detailed timing includes the native pixel format and preferred
> > >>>>     refresh rate.
> > >>>>
> > >>>>     ...
> > >>>>
> > >>>>     Detailed Timing Descriptors:
> > >>>>       DTD 1:  1920x1080  143.981 Hz  16:9   166.587 kHz  346.500 MHz
> > >>>>                    Hfront   48 Hsync  32 Hback  80 Hpol N
> > >>>>                    Vfront    3 Vsync   5 Vback  69 Vpol N
> > >>>>       DTD 2:  1920x1080   59.990 Hz  16:9    69.409 kHz  144.370 MHz
> > >>>>                    Hfront   48 Hsync  32 Hback  80 Hpol N
> > >>>>                    Vfront    3 Vsync   5 Vback  69 Vpol N
> > >>>>
> > >>>> I'm proposing here that the above is actually a bug and that the 60 Hz
> > >>>> mode really should be considered preferred by Linux.
> >
> > Its a bit tricky to say that this is a bug but I think we can certainly
> > add here that for an internal display we would have ideally had the
> > lower resolution first to indicate it as default.
> 
> Yeah, it gets into the vagueness of the EDID spec in general. As far
> as I can find it's really up to the monitor to decide by what means it
> chooses the "preferred" refresh rate if the monitor can support many.
> Some displays may decide that the normal rate is "preferred" and some
> may decide that the high refresh rate is "preferred". Neither display
> is "wrong" per say, but it's nice to have some consistency here and to
> make it so that otherwise "dumb" userspace will get something
> reasonable by default. I'll change it to say:
> 
> While the EDID spec appears to allow a display to use any criteria for
> picking which refresh mode is "preferred" or "optimal", that vagueness
> is a bit annoying. From Linux's point of view let's choose the 60 Hz
> one as the default.

And if we start making that decision, it should be for all panels with a
similar constraint, so most likely handled by the core, and the new
policy properly documented.

Doing that just for a single panel is weird.

Maxime

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