Re: [PATCH v2 01/10] usb: dwc3: core: Allow glue layer to pass reference clock rate

[Varadarajan Narayanan <varadarajan.narayanan@oss.qualcomm.com>]

On Sun, Sep 06, 2026 at 07:52:40AM +0400, George Moussalem via B4 Relay wrote:
> From: George Moussalem <george.moussalem@outlook.com>
>
> Add ability to pass the reference clock rate from the glue layer to the
> DWC3 core driver. The core calculates the reference clock period and
> frame length adjustment based on the reference clock rate.
>
> In the flattened snsp-dwc3 model, it is currently not possible to pass a
> reference clock that differs from the default since:
> commit 613a2e655d4d ("usb: dwc3: core: Expose core driver as library")
>
> The new glue layers (incl. Qualcomm's) set the ignore_clocks_and_resets
> flag in dwc3_probe_data to true, which disables the core driver's clock
> management, thus it also doesn't acquire the reference clock from the
> devicetree needed in dwc3_ref_clk_period.
>
> There's an existing DT property 'snps,ref-clock-period-ns', but that's
> been deprecated. In addition, basing the rate from the period is often
> not accurate enough to derive the frame length adjustment value.
>
> This prevents moving chipsets such as IPQ5018, IPQ6018, IPQ5332, IPQ5424
> and IPQ9574 with a reference clock rate that computes values for the
> period and frame length adjustment different from the hardware default
> from moving to the flattened model.
>
> So, add ability to set the reference clock rate in dwc3_probe_data, then
> have the core obtain the clock rate and use that to calculate the
> required period and frame length adjustment.
>
> Signed-off-by: George Moussalem <george.moussalem@outlook.com>

Reviewed-by: Varadarajan Narayanan <varadarajan.narayanan@oss.qualcomm.com>