Hi, On Thu, Feb 15, 2024 at 2:24 AM Jani Nikula <jani.nikula@xxxxxxxxx> wrote: > > On Wed, 14 Feb 2024, Doug Anderson <dianders@xxxxxxxxxxxx> wrote: > > Hi, > > > > On Tue, Feb 13, 2024 at 10:25 PM Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> wrote: > >> > >> On Wed, Feb 14, 2024 at 2:23 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > >> > > >> > If an eDP panel is not powered on then any attempts to talk to it over > >> > the DP AUX channel will timeout. Unfortunately these attempts may be > >> > quite slow. Userspace can initiate these attempts either via a > >> > /dev/drm_dp_auxN device or via the created i2c device. > >> > > >> > Making the DP AUX drivers timeout faster is a difficult proposition. > >> > In theory we could just poll the panel's HPD line in the AUX transfer > >> > function and immediately return an error there. However, this is > >> > easier said than done. For one thing, there's no hard requirement to > >> > hook the HPD line up for eDP panels and it's OK to just delay a fixed > >> > amount. For another thing, the HPD line may not be fast to probe. On > >> > parade-ps8640 we need to wait for the bridge chip's firmware to boot > >> > before we can get the HPD line and this is a slow process. > >> > > >> > The fact that the transfers are taking so long to timeout is causing > >> > real problems. The open source fwupd daemon sometimes scans DP busses > >> > looking for devices whose firmware need updating. If it happens to > >> > scan while a panel is turned off this scan can take a long time. The > >> > fwupd daemon could try to be smarter and only scan when eDP panels are > >> > turned on, but we can also improve the behavior in the kernel. > >> > > >> > Let's let eDP panels drivers specify that a panel is turned off and > >> > then modify the common AUX transfer code not to attempt a transfer in > >> > this case. > >> > > >> > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > >> > --- > >> > >> Reviewed-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> > > > > Thanks for the review! > > > > Given that this touches core DRM code and that I never got > > confirmation that Jani's concerns were addressed with my previous > > response, I'm still going to wait a little while before applying. I'm > > on vacation for most of next week, but if there are no further replies > > between now and then I'll plan to apply this to "drm-misc-next" the > > week of Feb 26th. If someone else wants to apply this before I do then > > I certainly won't object. Jani: if you feel this needs more discussion > > or otherwise object to this patch landing then please yell. Likewise > > if anyone else in the community wants to throw in their opinion, feel > > free. > > Sorry for dropping the ball after my initial response. I simply have not > had the time to look into this. > > It would be great to get, say, drm-misc maintainer ack on this before > merging. It's not fair for me to stall this any longer, I'll trust their > judgement. > > Reasonable? I'd be more than happy for one of the drm-misc maintainers to Ack. I'll move Maxime, Thomas, and Maarten to the "To:" line to see if that helps get through their filters. -Doug
