Re: [PATCH 5/5] arm64: dts: qcom: x1: disable ps883x USB4 capability

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The `parade,disable-usb4` property encodes a transient software workaround into the Device Tree and breaks non-fallback docks by intentionally failing retimer configuration.
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--- Patch [5]: [PATCH 5/5] arm64: dts: qcom: x1: disable ps883x USB4 capability ---
commit c967f56ff3b6574dc86834616a0288179a8a0cd3
Author: Jens Glathe <jens.glathe@oldschoolsolutions.biz>

arm64: dts: qcom: x1: disable ps883x USB4 capability

Add the "parade,disable-usb4" property to the PS883x node so that the
retimer driver treats USB4 as USB3. This allows the combo PHY to remain
in a DP-capable mode, restoring working DisplayPort output over the
dock while keeping USB functional.

[ ... ]

> diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> index 5d49df41be02a..c8bfb38c64ad5 100644
> --- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> +++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> @@ -895,6 +895,8 @@ typec-mux@8 {
>  		orientation-switch;
>  		retimer-switch;
>  
> +		parade,disable-usb4;

[Severity: High]
The commit message mentions this is a temporary platform workaround for missing
software support. Does this encode a transient OS driver limitation into the
device tree?

Device trees typically describe fixed hardware capabilities. Will adding this
property permanently mask the hardware's actual capabilities and cause issues 
for future OS updates once proper USB4 DP tunneling is available?

Also, looking at how the retimer driver handles this property:

drivers/usb/typec/mux/ps883x.c:ps883x_set() {
    ...
    case TYPEC_MODE_USB4:
        if (retimer->disable_usb4) {
            dev_info(&retimer->client->dev,
                     "USB4 disabled via DT property, rejecting USB4 mode\n");
            return -EOPNOTSUPP;
        }
    ...
}

By returning -EOPNOTSUPP, this intentionally skips retimer configuration and
leaves the physical link broken. While some docks might detect the broken
link, time out, and fall back to DP Alt Mode + USB3, what happens with docks
that don't implement this fallback behavior? 

Could this approach result in completely broken USB and DisplayPort
functionality on non-fallback docks when the PMIC autonomously negotiates
USB4?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260718-ps883x-disable-usb4-v1-0-cec86d0b909e@oldschoolsolutions.biz?part=5