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

Dmitry Baryshkov
2025-04-25T19:07:18Z

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@linaro.org>
> Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@gmail.com>
> Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
> ---
> drivers/gpu/drm/msm/dp/dp_ctrl.c | 126 ++++++++++++++++++++++---------
> 1 file changed, 89 insertions(+), 37 deletions(-)
>

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

--
With best wishes
Dmitry