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>]

On Sat, Aug 29, 2026, Marek Vasut wrote:
> On 8/29/26 12:40 AM, Thinh Nguyen wrote:
> 
> Hello Thinh,
> 
> > 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
> 
> I did that in V6.
> 
> > , 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.
> Could you please point me to the code which filters the WIRELESS USB out ? I
> can't seem to find it in either DWC3 core or USB core, but maybe I am not
> looking for the right thing.
> 
> Thank you for your help !

You can find this in __dwc3_gadget_set_speed(). The switch statement
explicitly handles unsupported speeds, and setting the speed to
USB_SPEED_LOW or USB_SPEED_WIRELESS will trigger a complaint there.

BR,
Thinh