Messages in this thread | | | Date | Thu, 28 Jul 2022 10:34:19 -0700 | Subject | Re: [RFC PATCH] drm/edid: Make 144 Hz not preferred on Sharp LQ140M1JW46 | From | Abhinav Kumar <> |
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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.
>>>> >>>> The argument here is that this is a laptop panel and on a laptop we >>>> know power will always be a concern. Presumably even if someone using >>>> this panel wanted to use 144 Hz for some use cases they would only do >>>> so dynamically and would still want the default to be 60 Hz. >>>> >>>> Let's change the default to 60 Hz using a standard quirk. >>>> >>>> Signed-off-by: Douglas Anderson <dianders@chromium.org> >>> >>> Yes, we were aware that 144Hz was getting picked. We found that while >>> debugging the screen corruption issue. >>> >>> Well, yes power would be less with 60Hz but so will be the performance. >> >> What performance specifically will be less with 60 Hz? In general the >> sc7280 CPU is a bit memory-bandwidth constrained and the LCD refresh >> from memory is a non-trivial part of that. Reducing to 60 Hz will >> relieve some of the memory bandwidth pressure and will actually allow >> tasks on the CPU to run _faster_. I guess the downside is that some >> animations might be a little less smooth... > > I guess he is referring to something that is vblank sync'd running > faster than 60fps. > > but OTOH it is a bit of a waste for fbcon to be using 144Hz. And > there are enough android games that limit themselves to 30fps to save > your "phone" battery. So it seems a lot more sane to default to 60Hz > and let userspace that knows it wants more pick the 144Hz rate when > needed. > > BR, > -R
Yes i was referring to vblank synced apps.
> >> >> >>> The test teams have been validating with 144Hz so far so we are checking >>> internally with the team whether its OKAY to goto 60Hz now since that >>> kind of invalidates the testing they have been doing. >> >> You're worried that the panel itself won't work well at 60 Hz, or >> something else about the system won't? The whole system in general >> needs to work well with 60 Hz displays and I expect them to be much >> more common than 144 Hz displays. Quite honestly if switching to 60 Hz >> uncovers a problem that would be a huge benefit of landing this patch >> because it would mean we'd find it now rather than down the road when >> someone hooks up a different panel.
I was worried that it will invalidate the testing they did so far but since you have confirmed that you would prefer 60Hz to be more thoroughly tested than 144Hz, I have informed the internal teams of this change and given the heads up.
You can have my R-b for this change,
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
I would also wait to see if others have different thought about this.
>> >> -Doug
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