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

[Mike Looijmans]

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@xxxxxxxx>
> > ---
> >
> >   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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