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

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Message-ID: <8ee2ce74-dc6b-463a-ba95-ad25669a1179@topic.nl>
Date: Mon, 17 Mar 2025 07:21:21 +0100
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC: "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Michal Simek <michal.simek@....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 14-03-2025 22:14, Thinh Nguyen wrote:
> 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?

I don't understand your question. What "programming flow" are you 
referring to?

The reset sequence was just plain wrong, the issue is almost the same as 
the one described in this commit:
e0183b974d30 "net: mdiobus: Prevent spike on MDIO bus reset signal"

Note that I see this high-low-high-low double reset toggle in many 
Xilinx software drivers, they seem to teach that at the Xilinx academy 
or so.


>> 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?
Now you mention it, the comment never made any sense anyway.


>> -		gpiod_set_value_cansleep(reset_gpio, 1);
>>   		usleep_range(5000, 10000);
> Do we still need this usleep_range here?

Yes, this is the "reset active" time.



>
> BR,
> Thinh
>
>>   		gpiod_set_value_cansleep(reset_gpio, 0);
>>   		usleep_range(5000, 10000);
>> -- 
>> 2.43.0
>>
>>
>> Met vriendelijke groet / kind regards,
>>
>> Mike Looijmans
>>
>>

-- 
Mike Looijmans
System Expert

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