Re: [PATCH v2] usb: dwc3: qcom: Add delays in UTMI clock selection for Qscratch

[Mattijs Korpershoek <mkorpershoek@kernel.org>]

Hi Balaji,

Thank you for the patch.

On Fri, Jun 27, 2025 at 10:22, Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com> wrote:

> Added delays before and after setting the PIPE_UTMI_CLK_SEL and
> PIPE3_PHYSTATUS_SW bits in the Qscratch GENERAL_CFG register
> during UTMI clock selection for DWC3 on Qualcomm platforms.
>
> These delays help ensure proper timing and stability of the UTMI
> clock switching sequence, potentially avoiding race conditions or
> unstable PHY behavior during initialization.
>
> Tested on platforms using Qscratch-based DWC3 PHY configuration.
>
> This change is taken from this Linux kernel implementation:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/usb/dwc3/dwc3-qcom.c?id=a4333c3a6ba9ca9cff50a3c1d1bf193dc5489e1c

Thank you for mentioning this link, it's very helpful for the review.

>
> Signed-off-by: Balaji Selvanathan <balaji.selvanathan@oss.qualcomm.com>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

> ---
> Changes in v2:
> - Corrected typo in email id in Signed-off (in v1)
> - Link to v1: https://lore.kernel.org/u-boot/20250627044304.2223767-1-balaji.selvanathan@oss.qualcomm.com/
> ---
>  drivers/usb/dwc3/dwc3-generic.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/usb/dwc3/dwc3-generic.c b/drivers/usb/dwc3/dwc3-generic.c
> index 21452ad1569..4800eb64484 100644
> --- a/drivers/usb/dwc3/dwc3-generic.c
> +++ b/drivers/usb/dwc3/dwc3-generic.c
> @@ -460,9 +460,13 @@ static void dwc3_qcom_select_utmi_clk(void __iomem *qscratch_base)
>  	setbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
>  			  PIPE_UTMI_CLK_DIS);
>  
> +	udelay(100);
> +
>  	setbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
>  			  PIPE_UTMI_CLK_SEL | PIPE3_PHYSTATUS_SW);
>  
> +	udelay(100);
> +
>  	clrbits_le32(qscratch_base + QSCRATCH_GENERAL_CFG,
>  			  PIPE_UTMI_CLK_DIS);
>  }
> -- 
> 2.34.1