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From: Doug Anderson <dianders@chromium.org>
Date: Tue, 19 Mar 2024 14:00:14 -0700
Message-ID: <CAD=FV=W0k5U0i+Q_X_3HAviY-LXNrAw=PFjWDg+eej-Kq=0Y3w@mail.gmail.com>
Subject: Re: [PATCH] drm/dp: Clarify that wait_hpd_asserted() is not optional
 for panels
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>, dri-devel@lists.freedesktop.org, 
	linux-tegra@vger.kernel.org, Mikko Perttunen <mperttunen@nvidia.com>, 
	Jonathan Hunter <jonathanh@nvidia.com>, Thierry Reding <thierry.reding@gmail.com>, 
	Ankit Nautiyal <ankit.k.nautiyal@intel.com>, Daniel Vetter <daniel@ffwll.ch>, 
	David Airlie <airlied@gmail.com>, Imre Deak <imre.deak@intel.com>, 
	Jani Nikula <jani.nikula@intel.com>, Maxime Ripard <mripard@kernel.org>, linux-kernel@vger.kernel.org
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Hi,

On Tue, Mar 19, 2024 at 1:55=E2=80=AFPM Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> > >>>> -        * panel to finish powering on. This is an optional functi=
on.
> > >>>> +        * panel to finish powering on. It is optional for DP AUX =
controllers
> > >>>> +        * to implement this function but required for DP AUX endp=
oints (panel
> > >>>> +        * drivers) to call it after powering up but before doing =
AUX transfers.
> > >>>> +        * If a DP AUX controller does not implement this function=
 then it
> > >>>> +        * may still support eDP panels that use the AUX controlle=
r's built-in
> > >>>> +        * HPD signal by implementing a long wait for HPD in the t=
ransfer()
> > >>>> +        * callback, though this is deprecated.
> > >>>
> > >>> It doesn't cover a valid case when the panel driver handles HPD sig=
nal
> > >>> on its own.
> > >>>
> > >>
> > >> This doc is only for wait_for_hpd_asserted(). If panel driver handle=
s
> > >> HPD signal on its own, this will not be called. Do we need a doc for=
 that?
> > >
> > > This comment declares that this callback must be called by the panel
> > > driver: '...but required for DP AUX endpoints [...] to call it after
> > > powering up but before doing AUX transfers.'
> > >
> > > If we were to follow documentation changes from this patch, we'd have
> > > to patch panel-edp to always call wait_for_hpd_asserted, even if HPD
> > > GPIO is used. However this is not correct from my POV.
> > >
> >
> > hmmm I dont mind explicitly saying "unless the panel can independently
> > check the HPD state" but not required in my opinion because if panel wa=
s
> > capable of checking the HPD gpio (its self-capable) why would it even
> > call wait_for_hpd_asserted?
>
> I'm fine with the proposed change. Doug?
>
> >
> > I will let you and Doug discuss this but fwiw, I am fine without this
> > additional clarification. So the R-b stands with or without this
> > additional clause.

Adjusted wording in v2. Kept Abhniav's R-b. PTAL.

https://lore.kernel.org/r/20240319135836.v2.1.I521dad0693cc24fe4dd14cba0c70=
48d94f5b6b41@changeid