linux-kernel - Re: [PATCH v1] drm/msm/dp: use dp_hpd_plug_handle() and dp_hpd_unplug

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAA8EJppEWXnsQzDD1tdNuMb1ijEVtE7LQct9jt1fwVwMd8ch_Q@mail.gmail.com>
Date: Fri, 29 Mar 2024 00:50:02 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc: Stephen Boyd <swboyd@...omium.org>, Bjorn Andersson <andersson@...nel.org>, 
	Johan Hovold <johan@...nel.org>, Kuogee Hsieh <quic_khsieh@...cinc.com>, abel.vesa@...aro.org, 
	agross@...nel.org, airlied@...il.com, daniel@...ll.ch, dianders@...omium.org, 
	dri-devel@...ts.freedesktop.org, robdclark@...il.com, sean@...rly.run, 
	vkoul@...nel.org, quic_jesszhan@...cinc.com, quic_sbillaka@...cinc.com, 
	marijn.suijten@...ainline.org, freedreno@...ts.freedesktop.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] drm/msm/dp: use dp_hpd_plug_handle() and
 dp_hpd_unplug_handle() directly

On Thu, 28 Mar 2024 at 23:21, Abhinav Kumar <quic_abhinavk@...cinc.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@...cinc.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@...cinc.com>



-- 
With best wishes
Dmitry