From: Doug Anderson <dianders@chromium.org>
To: Maxime Ripard <maxime@cerno.tech>
Cc: Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@linux.ie>,
Abhinav Kumar <quic_abhinavk@quicinc.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>
Subject: Re: [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46
Date: Fri, 29 Jul 2022 12:57:40 -0700 [thread overview]
Message-ID: <CAD=FV=UKYksHjuVR27DPdUFFtJrQKB2KbT08qjeYLNW_3y_Mfg@mail.gmail.com> (raw)
In-Reply-To: <20220729164136.opucqg64qz4ypmvo@penduick>
Hi,
On Fri, Jul 29, 2022 at 9:41 AM Maxime Ripard <maxime@cerno.tech> wrote:
>
> On Fri, Jul 29, 2022 at 07:50:20AM -0700, Doug Anderson wrote:
> > On Fri, Jul 29, 2022 at 12:51 AM Maxime Ripard <maxime@cerno.tech> wrote:
> > >
> > > 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.
> >
> > Yeah, though having a "general policy" in the core can be problematic.
> >
> > In general I think panel EDIDs are only trustworthy as far as you can
> > throw them. They are notorious for having wrong and incorrect
> > information, which is why the EDID quirk list exists to begin with.
> > Trying to change how we're going to interpret all EDIDs, even all
> > EDIDs for eDP panels, seems like it will break someone somewhere.
> > Maybe there are EDIDs out there that were only ever validated at the
> > higher refresh rate and they don't work / flicker / cause digitizer
> > noise at the lower refresh rate. Heck, we've seen eDP panel vendors
> > that can't even get their checksum correct, so I'm not sure I want to
> > make a global assertion that all panels validated their "secondary"
> > display mode.
> >
> > In this particular case, we have validated that this particular Sharp
> > panel works fine at the lower refresh rate.
> >
> > I would also note that, as far as I understand it, ODMs actually can
> > request different EDIDs from the panel vendors. In the past we have
> > been able to get panel vendors to change EDIDs. Thus for most panels
> > I'd expect that we would discover this early, change the EDID default,
> > and be done with it. The case here is a little unusual in that by the
> > time we got involved and started digging into this panel too many were
> > created and nobody wants to throw away those old panels. This is why
> > I'm treating it as a quirk/bug. Really: we should have updated the
> > EDID of the panel but we're unable to in this case.
>
> You raise some good points, but most of the discussion around that patch
> were mostly around performances, power consumption and so on.
>
> This is very much a policy decision, and if there is some panel where
> the EDID reports 60Hz but is broken, then that panel should be the
> exception to the policy
>
> But doing it for a single panel is just odd
OK, fair enough. I'll abandon this patch at least as far as mainline
is concerned, then.
-Doug
next prev parent reply other threads:[~2022-07-29 19:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-21 22:23 [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46 Douglas Anderson
2022-07-22 16:37 ` Abhinav Kumar
2022-07-22 16:48 ` Doug Anderson
2022-07-22 17:36 ` Rob Clark
2022-07-28 17:34 ` Abhinav Kumar
2022-07-28 21:18 ` Doug Anderson
2022-07-29 7:51 ` Maxime Ripard
2022-07-29 14:50 ` Doug Anderson
2022-07-29 16:41 ` Maxime Ripard
2022-07-29 19:57 ` Doug Anderson [this message]
2022-08-15 6:45 ` Maxime Ripard
2022-08-17 23:45 ` Doug Anderson
2022-08-18 10:31 ` Jani Nikula
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