linux-kernel - Re: [PATCH v2 11/12] drm/msm/dp: drop the entire HPD state machine

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Message-ID: <7vgdlv3kqttwav3ckqlb6xul6o3dpob5iokyqtdvnk3vvfbx4x@kg2gajwovdzi>
Date: Sat, 9 Aug 2025 10:26:06 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jessica Zhang <jessica.zhang@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Dmitry Baryshkov <lumag@...nel.org>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Yongxing Mou <quic_yongmou@...cinc.com>
Subject: Re: [PATCH v2 11/12] drm/msm/dp: drop the entire HPD state machine

On Fri, Aug 08, 2025 at 05:35:23PM -0700, Jessica Zhang wrote:
> Since internal HPD IRQ event handling has been moved to being handled by
> the DRM framework detect() and hpd_notify() callbacks, there is no need
> for the MSM driver to track the HPD state separately.
> 
> Drop all references to the HPD state machine and replace existing checks
> with checks for link_ready or sink_count.

After this patch there should no more difference between 'internal_hpd'
and 'external_hpd' cases. However, the code still tries to make the
difference for some reason. There are several places where the driver
calls msm_dp_display_send_hpd_notification(), e.g.
msm_dp_hpd_unplug_handle(), msm_dp_display_process_hpd_high(), etc.
These functions are called from msm_dp_bridge_hpd_notify(), which means
that we can end up with the lock ups because of the event loops.

> 
> Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c    |  22 ------
>  drivers/gpu/drm/msm/dp/dp_ctrl.h    |   1 -
>  drivers/gpu/drm/msm/dp/dp_display.c | 148 +++++++++---------------------------
>  3 files changed, 34 insertions(+), 137 deletions(-)
> 

-- 
With best wishes
Dmitry