[PATCH v3 0/2] usb: dwc3: qcom: Keep USB 2.0 working in DisplayPort-only modes

[Joonhoe Kim <26rote@gmail.com>]

With a USB-C monitor in DisplayPort pin assignment C or E, the QMP
USB3-DP combo PHY gives all four lanes to DisplayPort and keeps its USB
PCS powered down. The USB 2.0 pair still works, and such monitors
often have a USB 2.0 hub, but the dwc3 controller still runs from the
USB3 PIPE clock. On Kaanapali the next xHCI reset in this state times
out ("Host halt failed, -110"). USB stays lost until the cable is
replugged.
Commit f546912bcac6 ("phy: qcom: qmp-combo: Move pipe_clk on/off to
common") keeps the pipe clock branch enabled. That is not enough here.

This series registers the dwc3 glue as a Type-C mode switch next to the
PHY, so that it gets the mode (it does not route any signals). In
DP-only modes it moves the controller to the UTMI clock, as
"qcom,select-utmi-as-pipe-clk" does statically, before the PHY
switches.

On Kaanapali the PHY becomes a mode switch with Balaji Kalkonda's
DisplayPort series [1]. The controller side for that SoC is a DTS
patch sent separately to the Qualcomm tree. Other SoCs whose PHY is
already a mode switch (e.g. SM8650, SM8750) may need the same property
on their controller node (not tested).

Related: "phy: qcom: qmp-combo: Leave the USB PCS alone in DP-only mode"
(suspend in DP-only mode, sent separately) [2] and commit 89aaaa26f698
("usb: typec: mux: fsa4480: Keep the USB 2.0 switch on in DP-only
modes") for boards with an FSA4480 on the USB 2.0 pair.

Patch 2 is on top of Filippo Falezza's "usb: dwc3: qcom: Restore UTMI
PIPE clock on resume" [3]. On SM7250 QSCRATCH loses its contents in
system suspend, so patch 2 reads the selected clock back from QSCRATCH
instead of caching it. On Kaanapali QSCRATCH keeps its contents. [3]
is still under review and may change; patch 2 will be rebased if it
does.

Vladyslav Tymoshchuk's VBUS override fix [4] also changed
dwc3_qcom_pm_suspend() and dwc3_qcom_pm_resume(). Its next version
moves the change to the dwc3 core, as Thinh suggested, so it should no
longer conflict with patch 2.

Both patches are for the USB tree. The Kaanapali DTS patch, sent
separately, must not be applied before patch 2: once the controller
node has "mode-switch", pmic_glink_altmode defers its probe until
dwc3-qcom registers the mux, which never happens without patch 2.

Patch 2 makes USB_DWC3_QCOM depend on TYPEC, so with the arm64
defconfig (TYPEC=m) dwc3-qcom is built as a module. With "mode-switch"
on the controller, pmic_glink_altmode then probes later, and its first
HPD event can arrive before the DisplayPort driver has enabled HPD on
the aux-hpd bridge. aux-hpd drops that event, so a monitor attached at
boot is not detected. Yongxing Mou's "drm/bridge: aux-hpd-bridge:
replay last HPD status on hpd_enable" [5] addresses this; it was seen
on X1E as well.

Tested on a Lenovo Y700 Gen 5 (TB323FU, Kaanapali) with the series and
[3] backported to v7.3, plus [2] and the fsa4480 commit; the boot test
also had a variant of [5]. On each DisplayPort entry the controller
switched to the UTMI clock before the PHY switched, and back to the PIPE
clock on the next USB state. The monitor's USB 2.0 hub enumerated after
each of 5 DisplayPort entries, 3 of them on a replug less than 2 s
after the unplug, and after each of 3 s2idle cycles with the monitor
attached. Two other plugs stopped in USB PD negotiation, before
DisplayPort was entered. With the monitor attached, rebooting worked
(2 times) and DisplayPort came up at boot (2 boots). In these tests
the mux state came after resume or needed no clock change, so the
recorded change was not applied on resume.

Changes in v3:
- Patch 1: drop the mode-switch line and disallow orientation-switch
  and retimer-switch (Krzysztof)
- Patch 1: say that the controller only needs the mode and does not
  route any signals (Krzysztof)
- Patch 2: rebase on [3]; compare with the clock selected in QSCRATCH
  instead of a cached value
- Drop the Kaanapali DTS patch from the series. It is sent on its own
  for the Qualcomm tree (Krzysztof)
- Patch 2: check the safe state before the altmode, as the safe and
  USB states can come with the DisplayPort altmode (Sashiko)
- Patch 2: always select the UTMI clock for pin assignment C or E
  (Sashiko)
- Patch 2: do not resume the glue from the mux callback. From the start
  of a runtime or system suspend until the core has resumed, only
  record the state, and apply it on resume (Sashiko)
- Patch 2: leave the clock select alone on nodes without a mux
- Patch 2: only record the state once remove has started
- Link to v2: https://lore.kernel.org/all/20261103135057.1682-1-26rote@gmail.com/

Changes in v2:
- Patch 1: use the common usb-switch schema
- Patch 2: switch back to the PIPE clock in the mux callback, when a
  USB state follows the safe state. v1 waited for the next role change,
  which can come before the mux state (Sashiko)
- Patch 2: keep the UTMI clock on a change of pin assignment while
  DisplayPort is active, as the PHY keeps its mode then
- Patch 2: while the glue is suspended for system sleep, only record
  the mux state and select the clock on resume
- Patch 2: depend on TYPEC || TYPEC=n. Skip the mux without
  CONFIG_TYPEC. The arm64 defconfig has USB_DWC3_QCOM=y and TYPEC=m,
  which failed to link (Sashiko). It now builds the glue as a module
- Patch 2: no change to the role notifier
- Patch 3: note the dependency on [1] for the PHY's "mode-switch"
- Patch 3: add Reviewed-by from Abel
- Link to v1: https://lore.kernel.org/all/20261102215121.738-1-26rote@gmail.com/

[1] https://lore.kernel.org/all/20261022-kaanapali_dp-v3-0-b5ae8e6083c3@oss.qualcomm.com/
[2] https://lore.kernel.org/all/20261103135051.1668-1-26rote@gmail.com/
[3] https://lore.kernel.org/all/20261027-dwc3-utmi-resume-v1-1-ca9f0aa65783@gmail.com/
[4] https://lore.kernel.org/all/20261022224220.480-1-tvlad744@gmail.com/
[5] https://lore.kernel.org/all/20260803-drm-usbdp-preboot-v1-1-2539b362be00@oss.qualcomm.com/

Joonhoe Kim (2):
  dt-bindings: usb: qcom,snps-dwc3: Add mode-switch
  usb: dwc3: qcom: Use the UTMI clock as PIPE clock in DisplayPort-only
    modes

 .../bindings/usb/qcom,snps-dwc3.yaml          |   5 +
 drivers/usb/dwc3/Kconfig                      |   1 +
 drivers/usb/dwc3/dwc3-qcom.c                  | 154 ++++++++++++++++--
 3 files changed, 142 insertions(+), 18 deletions(-)


base-commit: ddfe51b0a0f5dc9e415cc2c8ad8db17532dd426b
prerequisite-patch-id: a793fca7329dac964c21459f8d7a8b003d36d84d
--
2.43.0