linux-kernel - Re: [PATCH] usb: dwc3: Always deassert xilinx resets

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Message-ID: <be8a566a-163f-4d20-b712-67de6f63a6b5@linux.dev>
Date: Fri, 9 Jan 2026 10:52:18 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: "open list:DESIGNWARE USB3 DRD IP DRIVER" <linux-usb@...r.kernel.org>,
 Neal Frager <neal.frager@....com>, Michal Simek <michal.simek@....com>,
 open list <linux-kernel@...r.kernel.org>,
 "moderated list:ARM/ZYNQ ARCHITECTURE"
 <linux-arm-kernel@...ts.infradead.org>,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: Always deassert xilinx resets

On 1/8/26 19:49, Thinh Nguyen wrote:
> On Tue, Jan 06, 2026, Sean Anderson wrote:
>> If we don't have a usb3 phy we don't need to assert the core resets.
>> Deassert them even if we didn't assert them to support booting when the
>> bootloader never released the core from reset.
>> 
> 
>> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
>> ---
>> 
>>  drivers/usb/dwc3/dwc3-xilinx.c | 67 ++++++++++++++++------------------
>>  1 file changed, 32 insertions(+), 35 deletions(-)
>> 
> 
> This sounds like a fix. Does it need to be Cc Stable and backported?

No, it's not a fix since the bootloaders currently in use on this
platform always initialize the serdes. But I want to add support for
skipping this initialization and this patch is necessary for that.

--Sean

> Regardless,
> 
> Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
> 
> Thanks,
> Thinh
> 
>> diff --git a/drivers/usb/dwc3/dwc3-xilinx.c b/drivers/usb/dwc3/dwc3-xilinx.c
>> index 0a8c47876ff9..f41b0da5e89d 100644
>> --- a/drivers/usb/dwc3/dwc3-xilinx.c
>> +++ b/drivers/usb/dwc3/dwc3-xilinx.c
>> @@ -132,21 +132,6 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>>  		goto err;
>>  	}
>>  
>> -	/*
>> -	 * The following core resets are not required unless a USB3 PHY
>> -	 * is used, and the subsequent register settings are not required
>> -	 * unless a core reset is performed (they should be set properly
>> -	 * by the first-stage boot loader, but may be reverted by a core
>> -	 * reset). They may also break the configuration if USB3 is actually
>> -	 * in use but the usb3-phy entry is missing from the device tree.
>> -	 * Therefore, skip these operations in this case.
>> -	 */
>> -	if (!priv_data->usb3_phy) {
>> -		/* Deselect the PIPE Clock Select bit in FPD PIPE Clock register */
>> -		writel(PIPE_CLK_DESELECT, priv_data->regs + XLNX_USB_FPD_PIPE_CLK);
>> -		goto skip_usb3_phy;
>> -	}
>> -
>>  	crst = devm_reset_control_get_exclusive(dev, "usb_crst");
>>  	if (IS_ERR(crst)) {
>>  		ret = PTR_ERR(crst);
>> @@ -171,22 +156,31 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>>  		goto err;
>>  	}
>>  
>> -	ret = reset_control_assert(crst);
>> -	if (ret < 0) {
>> -		dev_err(dev, "Failed to assert core reset\n");
>> -		goto err;
>> -	}
>> +	/*
>> +	 * Asserting the core resets is not required unless a USB3 PHY is used.
>> +	 * They may also break the configuration if USB3 is actually in use but
>> +	 * the usb3-phy entry is missing from the device tree. Therefore, skip
>> +	 * a full reset cycle and just deassert the resets if the phy is
>> +	 * absent.
>> +	 */
>> +	if (priv_data->usb3_phy) {
>> +		ret = reset_control_assert(crst);
>> +		if (ret < 0) {
>> +			dev_err(dev, "Failed to assert core reset\n");
>> +			goto err;
>> +		}
>>  
>> -	ret = reset_control_assert(hibrst);
>> -	if (ret < 0) {
>> -		dev_err(dev, "Failed to assert hibernation reset\n");
>> -		goto err;
>> -	}
>> +		ret = reset_control_assert(hibrst);
>> +		if (ret < 0) {
>> +			dev_err(dev, "Failed to assert hibernation reset\n");
>> +			goto err;
>> +		}
>>  
>> -	ret = reset_control_assert(apbrst);
>> -	if (ret < 0) {
>> -		dev_err(dev, "Failed to assert APB reset\n");
>> -		goto err;
>> +		ret = reset_control_assert(apbrst);
>> +		if (ret < 0) {
>> +			dev_err(dev, "Failed to assert APB reset\n");
>> +			goto err;
>> +		}
>>  	}
>>  
>>  	ret = phy_init(priv_data->usb3_phy);
>> @@ -201,11 +195,15 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>>  		goto err;
>>  	}
>>  
>> -	/* Set PIPE Power Present signal in FPD Power Present Register*/
>> -	writel(FPD_POWER_PRSNT_OPTION, priv_data->regs + XLNX_USB_FPD_POWER_PRSNT);
>> -
>> -	/* Set the PIPE Clock Select bit in FPD PIPE Clock register */
>> -	writel(PIPE_CLK_SELECT, priv_data->regs + XLNX_USB_FPD_PIPE_CLK);
>> +	if (priv_data->usb3_phy) {
>> +		/* Set PIPE Power Present signal in FPD Power Present Register*/
>> +		writel(FPD_POWER_PRSNT_OPTION, priv_data->regs + XLNX_USB_FPD_POWER_PRSNT);
>> +		/* Set the PIPE Clock Select bit in FPD PIPE Clock register */
>> +		writel(PIPE_CLK_SELECT, priv_data->regs + XLNX_USB_FPD_PIPE_CLK);
>> +	} else {
>> +		/* Deselect the PIPE Clock Select bit in FPD PIPE Clock register */
>> +		writel(PIPE_CLK_DESELECT, priv_data->regs + XLNX_USB_FPD_PIPE_CLK);
>> +	}
>>  
>>  	ret = reset_control_deassert(crst);
>>  	if (ret < 0) {
>> @@ -225,7 +223,6 @@ static int dwc3_xlnx_init_zynqmp(struct dwc3_xlnx *priv_data)
>>  		goto err;
>>  	}
>>  
>> -skip_usb3_phy:
>>  	/* ulpi reset via gpio-modepin or gpio-framework driver */
>>  	reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
>>  	if (IS_ERR(reset_gpio)) {
>> -- 
>> 2.35.1.1320.gc452695387.dirty
>>