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Mon, 15 Aug 2022 02:45:55 -0400 (EDT) Date: Mon, 15 Aug 2022 08:45:43 +0200 From: Maxime Ripard To: Doug Anderson Subject: Re: [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46 Message-ID: <20220815064543.g7loqfb6rtwkookl@houat> References: <20220721152314.RFC.1.Ie333b3e4aff6e4a5b58c4aa805e030e561be8773@changeid> <269f2610-425b-f296-dcfc-89bdc2e1d587@quicinc.com> <5c8ca71c-5f0b-d5f5-9f16-e312dec0d01b@quicinc.com> <20220729075118.ofnpk52tk4usm3n3@penduick> <20220729164136.opucqg64qz4ypmvo@penduick> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="wzbntj3bd7k5xk65" Content-Disposition: inline In-Reply-To: X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sankeerth Billakanti , Thomas Zimmermann , David Airlie , Abhinav Kumar , dri-devel , LKML , freedreno Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" --wzbntj3bd7k5xk65 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jul 29, 2022 at 12:57:40PM -0700, Doug Anderson wrote: > Hi, >=20 > On Fri, Jul 29, 2022 at 9:41 AM Maxime Ripard 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 wr= ote: > > > > > > > > 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 > > > > > 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 wrote: > > > > > > >> > > > > > > >> Hi, > > > > > > >> > > > > > > >> On Fri, Jul 22, 2022 at 9:37 AM Abhinav Kumar 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 EDI= D 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 3= 46.500 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 1= 44.370 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 th= at 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 c= ertainly > > > > > > 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 mea= ns it > > > > > chooses the "preferred" refresh rate if the monitor can support m= any. > > > > > Some displays may decide that the normal rate is "preferred" and = some > > > > > may decide that the high refresh rate is "preferred". Neither dis= play > > > > > is "wrong" per say, but it's nice to have some consistency here a= nd 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 criteri= a for > > > > > picking which refresh mode is "preferred" or "optimal", that vagu= eness > > > > > 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 w= ith 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 >=20 > OK, fair enough. I'll abandon this patch at least as far as mainline > is concerned, then. That wasn't really my point though :) If you think that this change is needed, then we should totally discuss it and I'm not opposed to it. What I don't really like about this patch is that it's about a single panel: if we're doing it we should do it for all the panels. Where we do it can also be discussed, but we should remain consistent there. Maxime --wzbntj3bd7k5xk65 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYvnrlwAKCRDj7w1vZxhR xaVpAQCkpLNIcSznLiwriHSHcXQmxwAgbpV0rZ1L2Xvo43kqVQD/RVC2++yCix/1 0Wq6Wm6rhIe0Cq+R41OyyQASUA2w4gM= =Qk4w -----END PGP SIGNATURE----- --wzbntj3bd7k5xk65--