Re: [PATCH v5 2/2] usb: dwc3: dwc3-generic-plat: Add Renesas R-Car Gen5 DWC3 xHCI USB controller glue

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

Hi Marek,

On Fri, Aug 28, 2026, Marek Vasut wrote:
> On 8/28/26 8:30 PM, sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > - [High] Missing 'maximum-speed' DT property incorrectly forces the controller into USB 2.0-only mode, overriding PHY-based detection.
> > --
> > 
> > commit 0727bb2cc9c155e4d5497db94c337bc5b2603464
> > Author: Thanh Quan <thanh.quan.xn@renesas.com>
> > usb: dwc3: dwc3-generic-plat: Add Renesas R-Car Gen5 DWC3 xHCI USB controller glue
> > 
> > This commit extends the generic DWC3 platform driver with glue logic for
> > Renesas R-Car Gen5 USB controllers. It handles hardware initialization and
> > evaluates PHY presence alongside device tree properties to determine maximum
> > supported USB speeds.
> > 
> > > diff --git a/drivers/usb/dwc3/dwc3-generic-plat.c b/drivers/usb/dwc3/dwc3-generic-plat.c
> > > index ca69ac0eb07ce..3994a6d93b9de 100644
> > > --- a/drivers/usb/dwc3/dwc3-generic-plat.c
> > > +++ b/drivers/usb/dwc3/dwc3-generic-plat.c
> > [ ... ]
> > > @@ -71,6 +71,55 @@ static int dwc3_eic7700_init(struct dwc3_generic *dwc3g)
> > >   	return 0;
> > >   }
> > > +static int dwc3_renesas_rcar_gen5_init(struct dwc3_generic *dwc3g)
> > > +{
> > > +	struct device *dev = dwc3g->dev;
> > > +	struct platform_device *pdev = to_platform_device(dev);
> > > +	enum usb_device_speed speed = usb_get_maximum_speed(dev);
> > > +	bool usb2only = false;
> > > +	void __iomem *glue;
> > > +
> > > +	/* Wireless USB is not supported */
> > > +	if (speed == USB_SPEED_WIRELESS)
> > > +		return dev_err_probe(dev, -EINVAL, "Wireless USB not supported\n");
> > > +
> > > +	/* No USB 3 PHY in DT means this is surely USB 2 controller */
> > > +	if (device_property_match_string(dev, "phy-names", "usb3-phy") < 0)
> > > +		usb2only = true;
> > > +
> > > +	if (speed <= USB_SPEED_HIGH)
> > > +		usb2only = true;
> > 
> > [Severity: High]
> > Will this condition inadvertently force the controller into USB 2.0 mode when
> > the maximum-speed property is missing from the device tree?
> > 
> > When the maximum-speed property is absent, usb_get_maximum_speed() returns
> > USB_SPEED_UNKNOWN, which evaluates to 0. Since 0 is less than USB_SPEED_HIGH,
> > this condition evaluates to true and unconditionally sets usb2only to true.

Right. I missed that.

> > 
> > This appears to override the preceding logic that correctly checked the
> > phy-names property to detect USB 3 capabilities. Could this cause hardware
> > with a USB 3 PHY to be improperly downgraded to USB 2.0 mode?
> 
> Thinh, maybe I should restore the V4 conditional here ?

Sure, but please drop the speed == USB_SPEED_WIRELESS check. This sanity
check is not necessary and would be flagged by dwc3 core if set anyway.

Thanks,
Thinh