linux-kernel - Re: [PATCH] usb: dwc3: xilinx: Prevent spike in reset signal

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Message-ID: <20250314211411.l5taj5nysvcalfyz@synopsys.com>
Date: Fri, 14 Mar 2025 21:14:25 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Mike Looijmans <mike.looijmans@...ic.nl>
CC: "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Simek <michal.simek@....com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: xilinx: Prevent spike in reset signal

On Fri, Mar 14, 2025, Mike Looijmans wrote:
> Set the gpio to "high" on acquisition, instead of acquiring it in low
> state and then immediately setting it high again. This prevents a
> short "spike" on the reset signal.

How does this affect the current programming flow beside preventing a
spike to the reset signal?

> 
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
> ---
> 
>  drivers/usb/dwc3/dwc3-xilinx.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
> index a33a42ba0249..a159a511483b 100644
> --- a/drivers/usb/dwc3/dwc3-xilinx.c
> +++ b/drivers/usb/dwc3/dwc3-xilinx.c
> @@ -207,7 +207,7 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>  
>  skip_usb3_phy:
>  	/* ulpi reset via gpio-modepin or gpio-framework driver */
> -	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
> +	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
>  	if (IS_ERR(reset_gpio)) {
>  		return dev_err_probe(dev, PTR_ERR(reset_gpio),
>  				     "Failed to request reset GPIO\n");
> @@ -215,7 +215,6 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>  
>  	if (reset_gpio) {
>  		/* Toggle ulpi to reset the phy. */

Does the comment above still apply?

> -		gpiod_set_value_cansleep(reset_gpio, 1);
>  		usleep_range(5000, 10000);

Do we still need this usleep_range here?

BR,
Thinh

>  		gpiod_set_value_cansleep(reset_gpio, 0);
>  		usleep_range(5000, 10000);
> -- 
> 2.43.0
> 
> 
> Met vriendelijke groet / kind regards,
> 
> Mike Looijmans
> System Expert
> 
> 
> TOPIC Embedded Products B.V.
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