linux-kernel - Re: [PATCH] drm/dp: Don't attempt AUX transfers when eDP panels are not powered

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Message-ID: <CAD=FV=VQvC+JxVgtm=w8jFf+_caUoH=6QsKdfP5zzDFwORgC-Q@mail.gmail.com>
Date: Wed, 28 Feb 2024 12:48:10 -0800
From: Doug Anderson <dianders@...omium.org>
To: neil.armstrong@...aro.org
Cc: Jani Nikula <jani.nikula@...el.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Hsin-Yi Wang <hsinyi@...omium.org>, dri-devel@...ts.freedesktop.org, eizan@...omium.org, 
	Ankit Nautiyal <ankit.k.nautiyal@...el.com>, Daniel Vetter <daniel@...ll.ch>, 
	David Airlie <airlied@...il.com>, Heiner Kallweit <hkallweit1@...il.com>, 
	Imre Deak <imre.deak@...el.com>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Sam Ravnborg <sam@...nborg.org>, Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/dp: Don't attempt AUX transfers when eDP panels are
 not powered

Hi,

On Wed, Feb 28, 2024 at 8:52 AM <neil.armstrong@...aro.org> wrote:
>
> On 28/02/2024 17:40, Doug Anderson wrote:
> > Neil,
> >
> > On Thu, Feb 15, 2024 at 8:53 AM Neil Armstrong
> > <neil.armstrong@...aro.org> wrote:
> >>
> >> Hi Doug,
> >>
> >> On 15/02/2024 16:08, Doug Anderson wrote:
> >>> Hi,
> >>>
> >>> On Thu, Feb 15, 2024 at 2:24 AM Jani Nikula <jani.nikula@...el.com> wrote:
> >>>>
> >>>> On Wed, 14 Feb 2024, Doug Anderson <dianders@...omium.org> wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On Tue, Feb 13, 2024 at 10:25 PM Hsin-Yi Wang <hsinyi@...omium.org> wrote:
> >>>>>>
> >>>>>> On Wed, Feb 14, 2024 at 2:23 PM Douglas Anderson <dianders@...omium.org> 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@...omium.org>
> >>>>>>> ---
> >>>>>>
> >>>>>> Reviewed-by: Hsin-Yi Wang <hsinyi@...omium.org>
> >>>>>
> >>>>> 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.
> >>
> >> I'll like some test reports to be sure it doesn't break anything,
> >> then I'll be happy to give my ack !
> >
> > Are you looking for any more test reports at this point? Eizan did
> > some testing and provided a tag, though this was also on ChromeOS.
> > Steev also tested on two non-ChromeOS environments and provided his
> > tag. It's also been another two weeks of this being rolled out to some
> > Chromebook users and I haven't heard any reports of problems. If
> > somehow something was missed, I'm happy to follow-up and provide
> > additional fixes if some report comes in later.
>
> Sure, thx I think you can apply it now
>
> Acked-by: Neil Armstrong <neil.armstrong@...aro.org>

Pushed to drm-misc-next.

8df1ddb5bf11 drm/dp: Don't attempt AUX transfers when eDP panels are not powered