Re: [PATCH] Revert "drivers: usb: dwc3: Add delay after core soft reset"

[Mattijs Korpershoek <mkorpershoek@kernel.org>]

Hi Balaji,

Thank you for the patch.

On Fri, Jul 24, 2026 at 14:58, Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com> wrote:

> This reverts commit 6de333b5caf035c38d7af9fa7596aeffcc49db42.
>
> The delay is unnecessary. Upstream Linux does not add this delay after
> the core soft reset and the USB works fine without it.
>
> Tested in QCS6490 RB3Gen2 Qualcomm board.
>
> Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>
> ---
> - This is part of ongoing initiative to reduce boot time across all
>   Qualcomm boards. So we can remove this unnecessary delay.
> - Actually, this delay was removed in the Kodiak v4 series:
>   https://lore.kernel.org/u-boot/20260418-kodiak_ss-v4-0-d381670c9d78@oss.qualcomm.com/
>   but v3 series got picked up: https://lore.kernel.org/u-boot/177745255938.126665.16625119085748603933.b4-ty@b4/
> ---
>  drivers/usb/dwc3/core.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index be198041f08..ae22e1c792d 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -106,8 +106,6 @@ done:
>  	if (DWC3_VER_IS_WITHIN(DWC31, ANY, 180A))
>  		mdelay(50);
>  
> -	mdelay(100);
> -

The dwc3 driver is not only used by qualcomm, but many other SoCs.

That delay indeed does not exist as is in the Linux driver since the
following commit f59dcab17629 ("usb: dwc3: core: improve reset sequence")

However, that commit is more conservative by adding retries and such.

I'd prefer to stick with Linux's approach here.

Also note, there is an ongoing effort of updating the dwc3 driver by
Linaro here:

https://lore.kernel.org/all/20260716134305.614278-1-anders.roxell@linaro.org/

Could you maybe give that a try? It should have the
"usb: dwc3: core: improve reset sequence" patch in there.

>  	return 0;
>  }
>  
>
> ---
> base-commit: d7ef23c07b8e34f65b3e15e3b4e7f58d074923c8
> change-id: 20260724-kodiak_delay-a5f1e8b675cd
>
> Best regards,
> -- 
> Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>