linux-kernel - Re: [PATCH v3 4/4] drm/msm/dp: Introduce link training per-segment for LTTPRs

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Message-ID: <zb5fqcnersry6blohozlzc3f2it2q6ypi4xei3z2fvzp5ogszj@mj23wsa64nqi>
Date: Fri, 25 Apr 2025 22:07:12 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Aleksandrs Vinarskis <alex.vinarskis@...il.com>
Cc: Dmitry Baryshkov <lumag@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        laurentiu.tudor1@...l.com, abel.vesa@...aro.org, johan@...nel.org,
        Stefan Schmidt <stefan.schmidt@...aro.org>
Subject: Re: [PATCH v3 4/4] drm/msm/dp: Introduce link training per-segment
 for LTTPRs

On Thu, Apr 17, 2025 at 04:10:35AM +0200, Aleksandrs Vinarskis wrote:
> DisplayPort requires per-segment link training when LTTPR are switched
> to non-transparent mode, starting with LTTPR closest to the source.
> Only when each segment is trained individually, source can link train
> to sink.
> 
> Implement per-segment link traning when LTTPR(s) are detected, to
> support external docking stations. On higher level, changes are:
> 
> * Pass phy being trained down to all required helpers
> * Run CR, EQ link training per phy
> * Set voltage swing, pre-emphasis levels per phy
> 
> This ensures successful link training both when connected directly to
> the monitor (single LTTPR onboard most X1E laptops) and via the docking
> station (at least two LTTPRs).
> 
> Tested-by: Stefan Schmidt <stefan.schmidt@...aro.org>
> Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@...il.com>
> Reviewed-by: Abel Vesa <abel.vesa@...aro.org>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 126 ++++++++++++++++++++++---------
>  1 file changed, 89 insertions(+), 37 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>

-- 
With best wishes
Dmitry