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From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date: Fri, 29 Mar 2024 00:50:02 +0200
Message-ID: <CAA8EJppEWXnsQzDD1tdNuMb1ijEVtE7LQct9jt1fwVwMd8ch_Q@mail.gmail.com>
Subject: Re: [PATCH v1] drm/msm/dp: use dp_hpd_plug_handle() and
 dp_hpd_unplug_handle() directly
To: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: Stephen Boyd <swboyd@chromium.org>, Bjorn Andersson <andersson@kernel.org>, 
	Johan Hovold <johan@kernel.org>, Kuogee Hsieh <quic_khsieh@quicinc.com>, abel.vesa@linaro.org, 
	agross@kernel.org, airlied@gmail.com, daniel@ffwll.ch, dianders@chromium.org, 
	dri-devel@lists.freedesktop.org, robdclark@gmail.com, sean@poorly.run, 
	vkoul@kernel.org, quic_jesszhan@quicinc.com, quic_sbillaka@quicinc.com, 
	marijn.suijten@somainline.org, freedreno@lists.freedesktop.org, 
	linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
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On Thu, 28 Mar 2024 at 23:21, Abhinav Kumar <quic_abhinavk@quicinc.com> wrote:
>
>
>
> On 3/28/2024 1:58 PM, Stephen Boyd wrote:
> > Quoting Abhinav Kumar (2024-03-28 13:24:34)
> >> + Johan and Bjorn for FYI
> >>
> >> On 3/28/2024 1:04 PM, Kuogee Hsieh wrote:
> >>> For internal HPD case, hpd_event_thread is created to handle HPD
> >>> interrupts generated by HPD block of DP controller. It converts
> >>> HPD interrupts into events and executed them under hpd_event_thread
> >>> context. For external HPD case, HPD events is delivered by way of
> >>> dp_bridge_hpd_notify() under thread context. Since they are executed
> >>> under thread context already, there is no reason to hand over those
> >>> events to hpd_event_thread. Hence dp_hpd_plug_handle() and
> >>> dp_hpd_unplug_hanlde() are called directly at dp_bridge_hpd_notify().
> >>>
> >>> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
> >>> ---
> >>>    drivers/gpu/drm/msm/dp/dp_display.c | 5 +++--
> >>>    1 file changed, 3 insertions(+), 2 deletions(-)
> >>>
> >>
> >> Fixes: 542b37efc20e ("drm/msm/dp: Implement hpd_notify()")
> >
> > Is this a bug fix or an optimization? The commit text doesn't tell me.
> >
>
> I would say both.
>
> optimization as it avoids the need to go through the hpd_event thread
> processing.
>
> bug fix because once you go through the hpd event thread processing it
> exposes and often breaks the already fragile hpd handling state machine
> which can be avoided in this case.

Please add a description for the particular issue that was observed
and how it is fixed by the patch.

Otherwise consider there to be an implicit NAK for all HPD-related
patches unless it is a series that moves link training to the enable
path and drops the HPD state machine completely.

I really mean it. We should stop beating a dead horse unless there is
a grave bug that must be fixed.

>
> >>
> >> Looks right to me,
> >>
> >> Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>


-- 
With best wishes
Dmitry