Re: [PATCH v2 0/3] usb: dwc3: qcom: Keep USB 2.0 working in DisplayPort-only modes

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Tue, Nov 03, 2026, Joonhoe Kim wrote:
> 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. Such monitors often
> have a USB 2.0 hub. But the dwc3 controller still depends on 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 lets the controller be a Type-C mode switch next to the PHY
> and moves it to the UTMI clock, the way "qcom,select-utmi-as-pipe-clk"
> does statically, before the PHY switches to DP-only mode.
> 
> On Kaanapali the PHY becomes a mode switch with Balaji Kalkonda's
> DisplayPort series [1]; patch 3 is the controller side for the same
> SoC. 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 fixes sent separately: "phy: qcom: qmp-combo: Leave the USB PCS
> alone in DP-only mode" (suspend in DP-only mode) [2] and "usb: typec:
> mux: fsa4480: Keep the USB 2.0 switch on in DP-only modes" (boards with
> an FSA4480 on the USB 2.0 pair) [3].
> 
> Patch 2 conflicts with Vladyslav Tymoshchuk's "usb: dwc3: qcom: Defer
> VBUS override update during system suspend" [4] in
> dwc3_qcom_pm_suspend() and dwc3_qcom_pm_resume(). Both add a lock
> there. Like [4], the mux callback defers the QSCRATCH write while the
> glue is suspended for system sleep. On top of [4] the two locks can
> become one.
> 
> Patches 1-2 are for the USB tree. Patch 3 must not be applied before
> patch 2: with "mode-switch" on the controller and no mux registered by
> dwc3-qcom, pmic_glink_altmode defers its probe indefinitely.
> 
> Tested on a Lenovo Y700 Gen 5 (TB323FU, Kaanapali) with the series
> backported to v7.3, plus [2] and [3]. A USB-C monitor ran over 4-lane
> HBR3. Its USB 2.0 hub worked after 10 replugs and after a plug-in during
> s2idle. In the s2idle case the mux state came after resume, so the
> deferred clock switch was not exercised. With the monitor
> unplugged, a USB 3 stick enumerated at SuperSpeed. Quick replugs (under
> a second) worked 9 times out of 10. The other time no PD contract was
> made, so no alternate mode was entered.
> 
> 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://urldefense.com/v3/__https://lore.kernel.org/all/20261102215121.738-1-26rote@gmail.com/__;!!A4F2R9G_pg!YksTt8G_fqiWUQQ_PwsYBGRXdl6VqqTDWd2wikgoX8SgvenwmVlKWzlnwkd6rTZnTFYmByY8ANgOkYQjs1Y$ 
> 
> [1] https://urldefense.com/v3/__https://lore.kernel.org/all/20261022-kaanapali_dp-v3-0-b5ae8e6083c3@oss.qualcomm.com/__;!!A4F2R9G_pg!YksTt8G_fqiWUQQ_PwsYBGRXdl6VqqTDWd2wikgoX8SgvenwmVlKWzlnwkd6rTZnTFYmByY8ANgO7ae9gpE$ 
> [2] https://urldefense.com/v3/__https://lore.kernel.org/all/20261023123512.1912-1-26rote@gmail.com/__;!!A4F2R9G_pg!YksTt8G_fqiWUQQ_PwsYBGRXdl6VqqTDWd2wikgoX8SgvenwmVlKWzlnwkd6rTZnTFYmByY8ANgOBOrhEyU$ 
> [3] https://urldefense.com/v3/__https://lore.kernel.org/all/20261022165143.1327-1-26rote@gmail.com/__;!!A4F2R9G_pg!YksTt8G_fqiWUQQ_PwsYBGRXdl6VqqTDWd2wikgoX8SgvenwmVlKWzlnwkd6rTZnTFYmByY8ANgOFxAQjF4$ 
> [4] https://urldefense.com/v3/__https://lore.kernel.org/all/20261018143126.3978-1-tvlad744@gmail.com/__;!!A4F2R9G_pg!YksTt8G_fqiWUQQ_PwsYBGRXdl6VqqTDWd2wikgoX8SgvenwmVlKWzlnwkd6rTZnTFYmByY8ANgOPYhgXAc$ 
> 
> Joonhoe Kim (3):
>   dt-bindings: usb: qcom,snps-dwc3: Add mode-switch
>   usb: dwc3: qcom: Use the UTMI clock as PIPE clock in DisplayPort-only
>     modes
>   arm64: dts: qcom: kaanapali: Mark the USB controller as a Type-C mode
>     switch
> 
>  .../bindings/usb/qcom,snps-dwc3.yaml          |   3 +
>  arch/arm64/boot/dts/qcom/kaanapali.dtsi       |   1 +
>  drivers/usb/dwc3/Kconfig                      |   1 +
>  drivers/usb/dwc3/dwc3-qcom.c                  | 103 +++++++++++++++---
>  4 files changed, 95 insertions(+), 13 deletions(-)
> 
> 
> base-commit: 7649ba73f9e7e1e04d0b46213e39c79ae09dd55c
> -- 
> 2.43.0
> 

Can you address Sashiko's review comments?

Thanks,
Thinh