Hector Martin (@[email protected])

OMG how are some monitors this broken. I had a report from a user of a monitor that stops working after a screen poweroff/poweron. It turns out that when you power off the monitor at the screen and then power it on, it *glitches the HPD signal* which causes an extremely fast disconnect/reconnect cycle, which triggers some race conditions in our display stack/firmware interaction (I think). But it gets worse. If you sleep the screen in software, then wake it up again... it does the same thing! After the Mac starts sending the display a video signal again after a wakeup, the display *vanishes and then comes back* and then the Mac has to do a whole powerdown/powerup and modeset cycle again! On macOS, this causes excessively slow wake-up times, but at least the flow does work there and it does come back eventually. This is also a consequence of the lack of HPD debouncing in Apple's DCP firmware - if it ignored these fast glitches (which are not unique to this monitor, it seems like a rather pervasive problem and I know at least AMD cards debounce the signal) then none of this would happen. Why are monitors and display stacks this messed up...