Messages in this thread | | | Date | Tue, 26 Apr 2022 14:21:16 -0700 | Subject | Re: [RFC PATCH] drm/edid: drm_add_modes_noedid() should set lowest resolution as preferred | From | Abhinav Kumar <> |
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On 4/26/2022 1:52 PM, Doug Anderson wrote: > Hi, > > On Tue, Apr 26, 2022 at 1:46 PM Abhinav Kumar <quic_abhinavk@quicinc.com> wrote: >> >> On 4/26/2022 1:21 PM, Douglas Anderson wrote: >>> If we're unable to read the EDID for a display because it's corrupt / >>> bogus / invalid then we'll add a set of standard modes for the >>> display. When userspace looks at these modes it doesn't really have a >>> good concept for which mode to pick and it'll likely pick the highest >>> resolution one by default. That's probably not ideal because the modes >>> were purely guesses on the part of the Linux kernel. >>> >>> Let's instead set 640x480 as the "preferred" mode when we have no EDID. >>> >>> Signed-off-by: Douglas Anderson <dianders@chromium.org> >> >> drm_dmt_modes array is sorted but you are also relying on this check to >> eliminate the non-60fps modes >> >> 5611 if (drm_mode_vrefresh(ptr) > 61) >> 5612 continue; >> >> I am not sure why we filter out the modes > 61 vrefresh. >> >> If that check will remain this is okay. >> >> If its not, its not reliable that the first mode will be 640x480@60 > > I suspect that the check will remain. I guess I could try to do > something fancier if people want, but I'd be interested in _what_ > fancier thing I should do if so. Do we want the rule to remain that we > always prefer 640x480, or do we want to prefer the lowest resolution? > ...do we want to prefer 60 Hz or the lowest refresh rate? Do we do > this only for DP (which explicitly calls out 640x480 @60Hz as the best > failsafe) or for everything? > > For now, the way it's coded up seems reasonable (to me). It's the > lowest resolution _and_ it's 640x480 just because of the current > values of the table. I suspect that extra lower resolution failsafe > modes won't be added, but we can always change the rules here if/when > they are. > > -Doug
Alright, agreed. The way the API is today, I dont see anything getting broken with this.
So typically, as per spec, when a preferred mode is not set by the sink, the first entry becomes the preferred mode.
This also aligns with that expectation.
So FWIW,
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
We will test this one also out with our equipment, then give tested-by tags.
Thanks
Abhinav
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