Re: [PATCH 2/2] usb: dwc3: qcom: Allow the glue layer to pass ref_clk to the core

[Krzysztof Kozlowski <krzk@kernel.org>]

On Tue, Aug 25, 2026 at 10:38:33AM +0530, Varadarajan Narayanan wrote:
> The dwc3-qcom glue layer sets probe_data.ignore_clocks_and_resets before
> calling dwc3_core_probe(), so the DWC3 core does not acquire ref_clk on its
> own. This prevents dwc3_ref_clk_period() from programming GUCTL and GFLADJ
> from the reference clock rate.
> 
> The deprecated snps,ref-clock-period-ns property is not a suitable
> replacement on IPQ9650. Its 24 MHz reference clock has a period of about
> 41.66 ns, while using 41 ns makes the calculated FLADJ value become 0 and
> leaves the reference clock configuration incorrect.
> 
> Allow the Qualcomm glue driver to provide ref_clk to the DWC3 core for
> platforms that may need it.
> 
> Signed-off-by: Varadarajan Narayanan <varadarajan.narayanan@oss.qualcomm.com>
> ---
>  drivers/usb/dwc3/dwc3-qcom.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index ac68b4218b56..2d6de6469c1e 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -705,6 +705,13 @@ static int dwc3_qcom_probe(struct platform_device *pdev)
>  	probe_data.res = &res;
>  	probe_data.ignore_clocks_and_resets = true;
>  	probe_data.properties = DWC3_DEFAULT_PROPERTIES;
> +
> +	qcom->dwc.ref_clk = devm_clk_get_optional(dev, "ref_clk");
> +	if (IS_ERR_OR_NULL(qcom->dwc.ref_clk)) {
> +		qcom->dwc.ref_clk = NULL;
> +		dev_info(dev, "NOT setting dwc.ref_clk\n");

No need for a message. Why every device should receive it during probe?

Aren't existing other devices use name "ref"? Why are you coming with
completely different name? SNPS binding also asks for ref.

Best regards,
Krzysztof