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