Re: [PATCH v4 2/2] usb: dwc3: dwc3-generic-plat: Add Renesas R-Car Gen5 DWC3 xHCI USB controller glue

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

Hi,

On Wed, Aug 19, 2026, 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>
> ---
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> Cc: devicetree@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-renesas-soc@vger.kernel.org
> Cc: linux-usb@vger.kernel.org
> ---
> V2: Extend dwc3-generic-plat driver instead
> V3: Handle maximum-speed as optional property, test for USB 3 PHY
>     non-presence to determine whether the controller is USB 2 only,
>     consider optional maximum-speed DT property, but if it is missing
>     then default to maximum controller capabilities based on the
>     presence of PHY phandles.
> V4: No change
> ---
>  drivers/usb/dwc3/dwc3-generic-plat.c | 60 ++++++++++++++++++++++++++++
>  1 file changed, 60 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/dwc3-generic-plat.c b/drivers/usb/dwc3/dwc3-generic-plat.c
> index ca69ac0eb07ce..dec89b068291a 100644
> --- a/drivers/usb/dwc3/dwc3-generic-plat.c
> +++ b/drivers/usb/dwc3/dwc3-generic-plat.c
> @@ -71,6 +71,60 @@ 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;
> +
> +	/*
> +	 * Controller can be limited to USB 2 via optional maximum-speed DT
> +	 * property. If the DT property is not present, default to maximum
> +	 * controller capabilities.
> +	 */

Minor nit: This comment does not give any new info than what's
documented in the maximum-speed property, do we need to repeat it here?

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

We don't support low speed or wireless, just check for speed <=
USB_SPEED_HIGH should be sufficient. The rest looks fine.

Thanks,
Thinh

> +
> +	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);
> +
> +	return 0;
> +}
> +
>  static int dwc3_spacemit_k1_init(struct dwc3_generic *dwc3g)
>  {
>  	struct device *dev = dwc3g->dev;
> @@ -231,11 +285,17 @@ static const struct dwc3_generic_config eic7700_dwc3 =  {
>  	.properties = DWC3_DEFAULT_PROPERTIES,
>  };
>  
> +static const struct dwc3_generic_config renesas_rcar_gen5_dwc3 = {
> +	.init = dwc3_renesas_rcar_gen5_init,
> +	.properties = DWC3_DEFAULT_PROPERTIES,
> +};
> +
>  static const struct of_device_id dwc3_generic_of_match[] = {
>  	{ .compatible = "spacemit,k1-dwc3", &spacemit_k1_dwc3},
>  	{ .compatible = "spacemit,k3-dwc3", },
>  	{ .compatible = "fsl,ls1028a-dwc3", &fsl_ls1028_dwc3},
>  	{ .compatible = "eswin,eic7700-dwc3", &eic7700_dwc3},
> +	{ .compatible = "renesas,rcar-gen5-dwc3", &renesas_rcar_gen5_dwc3},
>  	{ .compatible = "starfive,jhb100-dwc3", },
>  	{ /* sentinel */ }
>  };
> -- 
> 2.53.0
>