Re: [PATCH v2 2/7] drivers: usb: dwc3: Add delay after core soft reset

[Sumit Garg <sumit.garg@kernel.org>]

On Mon, Nov 24, 2025 at 09:24:58PM +0530, Balaji Selvanathan wrote:
> Add a 100 ms delay after clearing the core soft reset bit to ensure
> the DWC3 controller has sufficient time to complete its reset
> sequence before subsequent register accesses.
> 
> Without this delay, USB initialization can fail on some Qualcomm
> platforms, particularly when using super-speed capable PHYs like
> the QMP USB3-DP Combo PHY on SC7280/QCM6490.
> 
> The change is taken from following upstream Linux implementation:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/dwc3/core.c?id=f88359e1588b85cf0e8209ab7d6620085f3441d9

If I understand correctly the kernel change here especially following
comment:

	/*
	 * Wait for internal clocks to synchronized. DWC_usb31 and
	 * DWC_usb32 may need at least 50ms (less for DWC_usb3). To
	 * keep it consistent across different IPs, let's wait up to
	 * 100ms before clearing GCTL.CORESOFTRESET.
	 */

the delay is required before clearing GCTL.CORESOFTRESET and not after
which your change seems to do. Also, here we aren't doing any role
switch too, right?

-Sumit

> 
> Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
> ---
> v2:
> - Gave correct commit id for linux implementation
> ---
>  drivers/usb/dwc3/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index 847fa1f82c3..ff0bca0dd8e 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -94,6 +94,8 @@ static int dwc3_core_soft_reset(struct dwc3 *dwc)
>  	reg &= ~DWC3_GCTL_CORESOFTRESET;
>  	dwc3_writel(dwc->regs, DWC3_GCTL, reg);
>  
> +	mdelay(100);
> +
>  	return 0;
>  }
>  
> -- 
> 2.34.1
>