linux-kernel - Re: [PATCH 0/4] drm/msm/dp: ST_DISPLAY

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Message-ID: <3b5fa433-e3a3-4c77-b502-096576ecc2e3@oss.qualcomm.com>
Date: Fri, 30 May 2025 10:50:58 -0700
From: Jessica Zhang <jessica.zhang@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <lumag@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>, Johan Hovold <johan@...nel.org>,
        Bjorn Andersson
 <quic_bjorande@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@....qualcomm.com>,
        linux-kernel@...r.kernel.org, Yongxing Mou <quic_yongmou@...cinc.com>
Subject: Re: [PATCH 0/4] drm/msm/dp: ST_DISPLAY_OFF hpd cleanup



On 5/30/2025 9:05 AM, Dmitry Baryshkov wrote:
> On Fri, 30 May 2025 at 02:15, Jessica Zhang
> <jessica.zhang@....qualcomm.com> wrote:
>>
>> HPD state machine in msm dp display driver manages the state transitions
>> between various HPD events and the expected state of driver to make sure
>> both match up.
>>
>> Although originally done with the intent of managing userspace interactions
>> and interactions with compliance equipment, over period of time,
>> changes to this piece of code has become quite difficult to manage.
>>
>> Although, unwinding this logic will take some time and will be spread over
>> various changes, to start things, this series tries to get rid of the
>> ST_DISPLAY_OFF state as firstly, its really not an hpd state but a state
>> of the display overall. Coupled with this, there are quite a few checks
>> in the current code, the origins of which need to be re-visited OR are unclear
>> which seem unlikely or redundant. With DP controller on newer chipsets supporting
>> multiple streams, this has become increasingly difficult to work with.
>>
>> This series removes the redundant state checks and simplifies the logic as an
>> attempt to get rid of this ST_DISPLAY_OFF state.
>>
>> Note: This series has been tested with sa8775p and sc7180 devices with multiple
>> monitors and also multiple dongles with no noticeable regressions.
>> Both of these devices use native DP PHY though. Hence, if this series can
>> be verified on some devices with USBC-DP combo PHY with the help of the other
>> developers, that will be great.
>>
>> ---
>> Changes in v2:
> 
> The series is not marked as v2 though.

Hi Dmitry,

Sorry for the confusion -- had pulled the v1 [1] using `b4 prep -F` but 
forgot to force the revision number to v2.

[1] https://patchwork.freedesktop.org/series/142010/#rev1

Thanks,

Jessica Zhang

> 
>> - Rebased on top of next-20250523
>> - Change atomic_enable() to return early if ST_DISCONENCT_PENDING
>>    instead of completely dropping the
>>    if (state != ST_DISPLAY_OFF && state != ST_MAINLINK_READY) check (Dmitry)
>>
>> ---
>> Abhinav Kumar (4):
>>        drm/msm/dp: remove redundant checks related to ST_DISPLAY_OFF in plug/irq_ipd handlers
>>        drm/msm/dp: Return early from atomic_enable() if ST_DISCONNECT_PENDING
>>        drm/msm/dp: replace ST_DISPLAY_OFF with power_on in msm_dp_hpd_unplug_handle()
>>        drm/msm/dp: remove ST_DISPLAY_OFF as a hpd_state
>>
>>   drivers/gpu/drm/msm/dp/dp_display.c | 19 +++----------------
>>   1 file changed, 3 insertions(+), 16 deletions(-)
>> ---
>> base-commit: daf70030586cf0279a57b58a94c32cfe901df23d
>> change-id: 20241202-hpd_display_off-6051aa510f23
>>
>> Best regards,
>> --
>> Jessica Zhang <jessica.zhang@....qualcomm.com>
>>
> 
> 
> --
> With best wishes
> 
> Dmitry