Re: [PATCH v6 2/2] usb: dwc3: dwc3-generic-plat: Add Renesas R-Car Gen5 DWC3 xHCI USB controller glue

[Krishna Kurapati <krishna.kurapati@oss.qualcomm.com>]

On 8/29/2026 12:11 AM, Marek Vasut wrote:
> From: Thanh Quan <thanh.quan.xn@renesas.com>
> 
> The Renesas R-Car Gen5 SoC contains multiple instances of DWC3 USB
> controller with glue logic wrapper around them. Extend the generic
> DWC3 platform driver with Renesas R-Car Gen5 glue logic specifics.
> 
> Signed-off-by: Thanh Quan <thanh.quan.xn@renesas.com>
> Co-developed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
> ---

[...]

> diff --git a/drivers/usb/dwc3/dwc3-generic-plat.c b/drivers/usb/dwc3/dwc3-generic-plat.c
> index ca69ac0eb07ce..e8586c40d5006 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;
> +

Why not just set the maximum-speed property to "high-speed" instead of 
checking for "usb3-phy". That would be more clean.

> +	if (speed >= USB_SPEED_LOW && speed <= USB_SPEED_HIGH)
> +		usb2only = true;

And this check can be removed as well if we use "maximum-speed" property 
in DT.

> +
> +	glue = devm_platform_ioremap_resource_byname(pdev, "glue");
> +	if (IS_ERR(glue))
> +		return PTR_ERR(glue);
> +
> +	/*
> +	 * The datasheet describes initialization procedure without full
> +	 * information about the registers. Therefore, the source code is
> +	 * based on the bare metal code shared by the board team.
> +	 */
> +	writew(0x211, glue + 0x26);
> +
> +	/* USB2 does need additional register programming. */
> +	if (!usb2only)
> +		return 0;
> +
> +	writew(0x11, glue + 0x81c);
> +	writew(0x0, glue + 0x81a);
> +	writew(0x1, glue + 0x802);
> +
> +	usleep_range(10000, 20000);
> +
> +	writew(0x0, glue + 0x802);
> +	writew(0x1, glue + 0x2a);
> +	writew(0x1, glue + 0x81a);
> +
> +	usleep_range(10000, 20000);
> +

Use #defines for register offsets and register values like in 
dwc3_eic7700_init.

Regards,
Krishna,