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

On Wed, Feb 28, 2024 at 8:52=E2=80=AFAM <neil.armstrong@linaro.org> wrote:
>
> On 28/02/2024 17:40, Doug Anderson wrote:
> > Neil,
> >
> > On Thu, Feb 15, 2024 at 8:53=E2=80=AFAM Neil Armstrong
> > <neil.armstrong@linaro.org> wrote:
> >>
> >> Hi Doug,
> >>
> >> On 15/02/2024 16:08, Doug Anderson wrote:
> >>> Hi,
> >>>
> >>> On Thu, Feb 15, 2024 at 2:24=E2=80=AFAM Jani Nikula <jani.nikula@inte=
l.com> wrote:
> >>>>
> >>>> On Wed, 14 Feb 2024, Doug Anderson <dianders@chromium.org> wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On Tue, Feb 13, 2024 at 10:25=E2=80=AFPM Hsin-Yi Wang <hsinyi@chrom=
ium.org> wrote:
> >>>>>>
> >>>>>> On Wed, Feb 14, 2024 at 2:23=E2=80=AFPM Douglas Anderson <dianders=
@chromium.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 propositi=
on.
> >>>>>>> In theory we could just poll the panel's HPD line in the AUX tran=
sfer
> >>>>>>> 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 f=
ixed
> >>>>>>> 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 b=
oot
> >>>>>>> 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 caus=
ing
> >>>>>>> real problems. The open source fwupd daemon sometimes scans DP bu=
sses
> >>>>>>> looking for devices whose firmware need updating. If it happens t=
o
> >>>>>>> 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 panel=
s 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 a=
nd
> >>>>>>> then modify the common AUX transfer code not to attempt a transfe=
r in
> >>>>>>> this case.
> >>>>>>>
> >>>>>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> >>>>>>> ---
> >>>>>>
> >>>>>> Reviewed-by: Hsin-Yi Wang <hsinyi@chromium.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 repl=
ies
> >>>>> 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 t=
hen
> >>>>> I certainly won't object. Jani: if you feel this needs more discuss=
ion
> >>>>> or otherwise object to this patch landing then please yell. Likewis=
e
> >>>>> if anyone else in the community wants to throw in their opinion, fe=
el
> >>>>> 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 befor=
e
> >>>> merging. It's not fair for me to stall this any longer, I'll trust t=
heir
> >>>> 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 tha=
t
> >>> 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@linaro.org>

Pushed to drm-misc-next.

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