Re: [PATCH v8 3/3] usb: dwc3: xilinx: Add ULPI PHY reset handling

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Hi Rob,

On 1/26/22 6:40 PM, Robert Hancock wrote:
> Hook up an optional GPIO-based reset for the connected USB ULPI PHY
> device. This is typically already done by the first-stage boot loader,
> however it can be more robust to ensure this reset is done prior to
> loading the driver in Linux.
> 
> Based on a patch "usb: dwc3: xilinx: Add gpio-reset support" in the
> Xilinx kernel tree by Piyush Mehta <piyush.mehta@xxxxxxxxxx>.
> 
> Signed-off-by: Robert Hancock <robert.hancock@xxxxxxxxxx>
> ---
>  drivers/usb/dwc3/dwc3-xilinx.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
> index a6f3a9b38789..1ee6011ada44 100644
> --- a/drivers/usb/dwc3/dwc3-xilinx.c
> +++ b/drivers/usb/dwc3/dwc3-xilinx.c
> @@ -11,6 +11,7 @@
>  #include <linux/slab.h>
>  #include <linux/clk.h>
>  #include <linux/of.h>
> +#include <linux/gpio/consumer.h>
>  #include <linux/platform_device.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/of_platform.h>
> @@ -101,6 +102,7 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>  	struct phy		*usb3_phy;
>  	int			ret = 0;
>  	u32			reg;
> +	struct gpio_desc        *reset_gpio;
>  
>  	usb3_phy = devm_phy_optional_get(dev, "usb3-phy");
>  	if (IS_ERR(usb3_phy)) {
> @@ -110,6 +112,14 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>  		goto err;
>  	}
>  
> +	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(reset_gpio)) {
> +		ret = PTR_ERR(reset_gpio);
> +		dev_err_probe(dev, ret,
> +			      "Failed to get reset gpio\n");
> +		goto err;
> +	}
> +
>  	/*
>  	 * The following core resets are not required unless a USB3 PHY
>  	 * is used, and the subsequent register settings are not required
> @@ -201,6 +211,15 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>  	}
>  
>  skip_usb3_phy:
> +	/* ulpi reset via gpio-modepin or gpio-framework driver */
> +	if (reset_gpio) {
> +		/* Toggle ulpi to reset the phy. */
> +		gpiod_set_value(reset_gpio, 0);
> +		usleep_range(5000, 10000); /* delay */
> +		gpiod_set_value(reset_gpio, 1);
> +		usleep_range(5000, 10000); /* delay */
> +	}
> +
>  	/*
>  	 * This routes the USB DMA traffic to go through FPD path instead
>  	 * of reaching DDR directly. This traffic routing is needed to
> 

Do we need to have this in dwc3? Why not just use the usb-nop-xceiv driver (aka usb_phy_generic)?

--Sean



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