Message-ID: <n2wt3i3lrbz2spfxdmkwvq6xdjq4rwif3sul755h6prs4w4fj5@ishlqsc4qxr2>
Date: Fri, 25 Apr 2025 01:14:19 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Rob Clark <robdclark@...il.com>
Cc: Aleksandrs Vinarskis <alex.vinarskis@...il.com>,
        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,
        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
Subject: Re: drm/msm/dp: Introduce link training per-segment for LTTPRs

On Thu, Apr 24, 2025 at 02:12:15PM -0700, Rob Clark wrote:
> On Wed, Apr 16, 2025 at 7:13 PM Aleksandrs Vinarskis
> <alex.vinarskis@...il.com> wrote:
> >
> > Recently added Initial LTTPR support in msm/dp has configured LTTPR(s)
> > to non-transparent mode to enable video output on X1E-based devices
> > that come with LTTPR on the motherboards. However, video would not work
> > if additional LTTPR(s) are present between sink and source, which is
> > the case for USB Type-C docks (eg. Dell WD19TB/WD22TB4), and at least
> > some universal Thunderbolt/USB Type-C monitors (eg. Dell U2725QE).
> >
> > First, take into account LTTPR capabilities when computing max link
> > rate, number of lanes. Take into account previous discussion on the
> > lists - exit early if reading DPCD caps failed. This also fixes
> > "*ERROR* panel edid read failed" on some monitors which seems to be
> > caused by msm_dp_panel_read_sink_caps running before LTTPR(s) are
> > initialized.
> >
> > Finally, implement link training per-segment. Pass lttpr_count to all
> > required helpers.
> > This seems to also partially improve UI (Wayland) hanging when
> > changing external display's link parameters (resolution, framerate):
> > * Prior to this series, via direct USB Type-C to display connection,
> >   attempt to change resolution or framerate hangs the UI, setting does
> >   not stick. Some back and forth replugging finally sets desired
> >   parameters.
> > * With this series, via direct USB Type-C to display connection,
> >   changing parameters works most of the time, without UI freezing. Via
> >   docking station/multiple LTTPRs the setting again does not stick.
> > * On Xorg changing link paramaters works in all combinations.
> >
> > These appear to be mainlink initialization related, as in all cases LT
> > passes successfully.
> >
> > Test matrix:
> > * Dell XPS 9345, Ubuntu 24.10, Gnome 47, Wayland (myself)
> >         * Left USB Type-C, Right USB Type-C
> >         * Direct monitor connection, Dell WD19TB, Dell WD22TB4, USB
> >           Type-C to HDMI dongle, USB Type-C to DP dongle
> >         * Dell AW3423DWF, Samsung LS24A600, dual Samsung LS24A600 (one
> >           monitor per USB Type-C connector)
> > * Dell XPS 9345, Ubuntu 24.10, Gnome 47, Wayland (myself)
> >         * Left USB Type-C, Right USB Type-C
> >         * Direct monitor connection
> >         * Samsung S34BG85 (USB Type-C), Dell U2725QE (universal
> >           Thunderbolt/USB Type-C, probes with an LTTPR when in USB
> >           Type-C/DP Alt mode)
> > * Dell XPS 9345, Debian trixie/sid, Gnome 48, Wayland (Stefan Schmidt)
> >         * Left USB Type-C, Right USB Type-C
> >         * Dell WD15 Dock with DisplayPort connected
> >         * Dell HD22Q dock with HDMI connected
> >         * USB Type-C to HDMI dongle
> >         * Dell U3417W
> 
> For the series,
> 
> Tested-by: Rob Clark <robdclark@...il.com>  # yoga slim 7x

Could you please send this as a response to one of the patches, so that
it's also recorded by the patchwork?

> 
> patch 4/4 had a number of conflicting hunks, you might need to rebase
> on msm-next
> 
> BR,
> -R
> 
> > In both cases, "Thunderbot Support"/"USB4 PCIE Tunneling" was disabled
> > in UEFI to force universal Thunderbolt/USB Type-C devices to work in
> > DP Alt mode.
> > In both cases laptops had HBR3 patches applied [1], resulting in
> > maximum successful link at 3440x1440@...hz and 4k@...z respectively.
> > When using Dell WD22TB4/U2725QE, USB Type-C pin assigment D got enabled
> > and USB3.0 devices were working in parallel to video ouput.
> >
> > Known issues:
> > * As mentioned above, it appears that on Gnome+Wayland framerate and
> >   resolution parameter adjustment is not stable.
> >
> > Due to lack of access to the official DisplayPort specfication, changes
> > were primarily inspired by/reverse engineered from Intel's i915 driver.
> >
> > [1] https://lore.kernel.org/all/20250226231436.16138-2-alex.vinarskis@gmail.com/
> >
> > Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@...il.com>
> >
> > ---
> >
> > Changes in v3:
> > - Split 1st patch into 3
> > - Simplified handling of max_lttpr_lanes/max_lttpr_rate
> > - Moved lttpr_common_caps to msm_dp_link (not msm_dp_panel, as LTTPRs
> >   are link related, not panel related)
> > - Picked Stefan's T-b tag (last patch only, as 1st one is getting split)
> > - Droped Abel's R-b tags from 1st patch that got split due to high diff
> > - Fixed alignment issues, initialization of variables, debug prints
> > - Moved lttpr_count to avoid ugly pointer
> > - Link to v2: https://lore.kernel.org/all/20250311234109.136510-1-alex.vinarskis@gmail.com/
> >
> > Changes in v2:
> > - Picked up Abel's R-b tags
> > - Fixed typo as per Abel, fixed readability as per Johan
> > - Updated cover and commit message on mailink issue which appears to be
> >   specific to Gnome+Wayland. No problems on Xorg.
> > - Link to v1: https://lore.kernel.org/all/20250310211039.29843-1-alex.vinarskis@gmail.com/
> >
> > Aleksandrs Vinarskis (4):
> >   drm/msm/dp: Fix support of LTTPR initialization
> >   drm/msm/dp: Account for LTTPRs capabilities
> >   drm/msm/dp: Prepare for link training per-segment for LTTPRs
> >   drm/msm/dp: Introduce link training per-segment for LTTPRs
> >
> >  drivers/gpu/drm/msm/dp/dp_ctrl.c    | 126 ++++++++++++++++++++--------
> >  drivers/gpu/drm/msm/dp/dp_display.c |  27 ++++--
> >  drivers/gpu/drm/msm/dp/dp_link.h    |   4 +
> >  drivers/gpu/drm/msm/dp/dp_panel.c   |  12 ++-
> >  4 files changed, 122 insertions(+), 47 deletions(-)
> >
> > --
> > 2.45.2
> >

-- 
With best wishes
Dmitry

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