Hello Aleksandrs,
On Wed, 12 Mar 2025 at 00:41, Aleksandrs Vinarskis
<alex.vinarskis@xxxxxxxxx> 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
> * 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
> * 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)
You can add the following:
* Dell XPS 9345, Debian trixie/sid, Gnome 48, Wayland
* 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
> 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@100hz and 4k@60hz 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.
I can confirm this on Gnome 48 + Wayland as well. Sometimes the resolution
change from gnome settings gets stuck and does not apply. It normally works
here around every third try or so when using a dock.
> 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@xxxxxxxxx/
>
> Signed-off-by: Aleksandrs Vinarskis <alex.vinarskis@xxxxxxxxx>
Tested-by: Stefan Schmidt <stefan.schmidt@xxxxxxxxxx>
regards
Stefan Schmidt
