On 30 June 2022 04:57:35 GMT+03:00, Rob Clark <robdclark@xxxxxxxxx> wrote: >On Wed, Jun 29, 2022 at 5:36 PM Doug Anderson <dianders@xxxxxxxxxxxx> wrote: >> >> Hi, >> >> On Tue, Jun 28, 2022 at 1:14 PM Dmitry Baryshkov >> <dmitry.baryshkov@xxxxxxxxxx> wrote: >> > >> > On 28 June 2022 18:20:06 GMT+03:00, Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx> wrote: >> > >Some userspace presumes that the first connected connector is the main >> > >display, where it's supposed to display e.g. the login screen. For >> > >laptops, this should be the main panel. >> > > >> > >This patch call drm_helper_move_panel_connectors_to_head() after >> > >drm_bridge_connector_init() to make sure eDP stay at head of >> > >connected connector list. This fixes unexpected corruption happen >> > >at eDP panel if eDP is not placed at head of connected connector >> > >list. >> > >> > The change itself is a good fix anyway. (And I'd ack it.) However I would like to understand why does it fix the corruption issue. What is we have eDP and DSI, with DSI ending up before the eDP? Would we see the issue? >> > Also could you please describe the mind of corruption you are observing? >> >> I've spent a whole bunch of time poking at this and in the end my >> conclusion is this: >> >> 1. The glitchyness seems to be a result of the Chrome OS userspace >> somehow telling the kernel to do something wrong. >> >> 2. I believe (though I have no proof other than Kuogee's patch fixing >> things) that the Chrome OS userspace is simply confused by the eDP >> connector being second. This would imply that Kuogee's patch is >> actually the right one. >> >> 3. It would be ideal if the Chrome OS userspace were fixed to handle >> this, but it's an area of code that I've never looked at. It also >> seems terribly low priority to fix since apparently other OSes have >> similar problems (seems like this code was originally added by >> RedHat?) >> >> >> Specifically, I tested with a similar but "persistent" glitch that I >> reproduced. The glitch Kuogee was digging into was a transitory glitch >> on the eDP (internal) display when you plugged in a DP (external) >> display. It would show up for a frame or two and then be fixed. I can >> get a similar-looking glitch (vertical black and white bars) that >> persists by doing these steps on a Chrome OS device (and Chrome OS >> kernel): >> >> a) Observe screen looks good. >> b) Observe DP not connected. >> c) Plug in DP >> d) See transitory glitch on screen, then it all looks fine. >> e) set_power_policy --ac_screen_dim_delay=5 --ac_screen_off_delay=10 >> f) Wait for screen to turn off >> g) Unplug DP >> h) Hit key on keyboard to wake device. >> i) See glitchy. >> j) Within 5 seconds: set_power_policy --ac_screen_dim_delay=5000 >> --ac_screen_off_delay=10000 >> >> Once I'm in the persistent glitch: >> >> * The "screenshot" command in Chrome OS shows corruption. Not exactly >> black and white bars, but the image produced has distinct bands of >> garbage. >> >> * I can actually toggle between VT2 and the main screen (VT1). Note >> that VT1/VT2 are not quite the normal Linux managed solution--I >> believe they're handled by frecon. In any case, when I switch to VT2 >> it looks normal (I can see the login prompt). Then back to VT1 and the >> vertical bars glitch. Back to VT2 and it's normal. Back to VT1 and the >> glitch again. This implies (especially with the extra evidence of >> screenshot) that the display controller hardware is all fine and that >> it's the underlying data that's somehow messed up. > >fwiw, from looking at this a bit w/ Doug, I think the "glitch" is >simply just an un-renderered buffer being interpreted by the display >controller as UBWC (because userspace tells it to) Thanks for the description. I think the userspace code should be fixed too, but this patch can go in on its own. Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> > >BR, >-R > >> When I pick Kuogee's patch then this "persistent" glitch goes away >> just like the transitory one does. >> >> I'm going to go ahead and do: >> >> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> >> Tested-by: Douglas Anderson <dianders@xxxxxxxxxxxx> -- With best wishes Dmitry
