Re: [PATCH 3/9] usb: dwc3: qcom: Add support for selecting UTMI as reference clock

[George Moussalem]

On 8/26/26 13:18, Konrad Dybcio wrote:
> On 8/25/26 12:42 PM, George Moussalem via B4 Relay wrote:
>> From: George Moussalem <george.moussalem@xxxxxxxxxxx>
>>
>> On many Qualcomm chipsets, the UTMI clock is used as the reference clock
>> (ex. IPQ5018, IPQ6018, and IPQ9574 and more). Since moving to the new
>> flattened snps-dwc3 model, it is no longer possible to pass the
>> reference clock to the dwc3 core driver.
>>
>> The clock rate is used by dwc3 core to derive the reference clock period
>> and frame length adjusment. This is needed when the reference clock
>> deviates from the hardware default (typically 19.2MHz). Above mentioned
>> SoCs use different rates and, as such, the core initializes with the
>> wrong values which leads to non-functional USB operation.
>>
>> Read the "qcom,select-utmi-as-ref-clk" property to determine if the UTMI
>> clock should be used as the reference clock. If so, set it as the
>> reference clock in the dwc3_probe_data structure.
>> The dwc3 core driver will then use this clock to derive the clock rate.
>>
>> Signed-off-by: George Moussalem <george.moussalem@xxxxxxxxxxx>
>> ---
> 
> There's a shorter patch in flight:
> 
> https://lore.kernel.org/linux-arm-msm/20260825-ctrl-v1-2-609e2291814d@xxxxxxxxxxxxxxxx/

I'm aware and have discussed that with Varada. My concerns are that
directly setting qcom->dwc->ref_clk from the glue layer is a layering
violation. This patch passes it to the DWC3 core via the probe_data struct.

In addition, if ignore_clocks_and_resets is set in the glue layer (which
is the case for qcom's and others), setting the dwc->ref_clk makes it
become managed by the core which is the opposite of what the
ignore_clocks_and_resets property is there for.

> 
> Konrad

George