Hi, On Mon, Mar 25, 2024 at 5:05 PM Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> wrote: > > On Mon, Mar 25, 2024 at 2:57 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > > > > If at boot we fail to power up the eDP panel (most often happens if > > the eDP panel never asserts HPD to us) or if we are unable to read the > > EDID at bootup to figure out the panel's ID then let's use the > > conservative eDP panel powerup/powerdown timings but _not_ fail the > > probe. > > > > It might seem strange to _not_ fail the probe in this case since we > > were unable to powerup the panel and confirm it's there. However, > > there is a reason to do this. Specifically, if we fail to probe the > > panel then it really throws the whole display pipeline for loop. Most > > DRM subsystems are written so that they wait until all components > > (including the panel) have probed before they set everything up. When > > the panel doesn't come up then this never happens. As a side effect of > > not setting everything up then other display adapters don't get > > initialized. As a practical example, I can see that if I open up a > > sc7180-trogdor based Chromebook that's using the generic "edp-panel" > > and unplug the eDP panel that it causes the _external_ DP monitor not > > to function. This is obviously bad because it means that a device with > > a dead eDP panel becomes e-waste when it could instead still be given > > useful life with an external display. > > > > NOTES: > > - When we fail to probe like this, boot is a bit slow because we try > > several times to power the panel up. This doesn't feel horrible > > because it'll eventually work and the retries are known to help > > bring some panels up. > > - In the case where we hit the condition of failing to power up, the > > display will likely _never_ have a chance to work again until > > reboot. Once the panel-edp pm_runtime resume function fails it > > doesn't ever seem to retry. This is probably for the best given that > > we don't have any real timing/modes. eDP isn't expected to be > > "hotplugged" so this makes some sense. > > - It turns out that this makes panel-edp behave more similarly for > > users of the generic "edp-panel" compatible string and the old fixed > > panel compatible string. With the old fixed panel compatible string > > we don't talk to the panel during probe so we'd actually behave much > > the same way that we'll now behave for the generic "edp-panel". > > > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > > Reviewed-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> Pushed to drm-misc-next: ce0ff22388ab drm/panel-edp: If we fail to powerup/get EDID, use conservative timings
