Re: [PATCH v2 4/6] usb: dwc3: reference clock period configuration

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

Rob Herring wrote:
> On Wed, Aug 04, 2021 at 05:22:27PM +0300, Baruch Siach wrote:
>> Hi Felipe,
>>
>> On Wed, Aug 04 2021, Felipe Balbi wrote:
>>> Baruch Siach <baruch@tkos.co.il> writes:
>>>> @@ -1371,6 +1398,8 @@ static void dwc3_get_properties(struct dwc3 *dwc)
>>>>  				    &dwc->hsphy_interface);
>>>>  	device_property_read_u32(dev, "snps,quirk-frame-length-adjustment",
>>>>  				 &dwc->fladj);
>>>> +	device_property_read_u32(dev, "snps,ref-clock-period",
>>>> +				 &dwc->ref_clk_per);
>>>
>>> I wonder if it would make more sense to pass an actual clock reference
>>> here. If valid, then reconfigure the period to the value returned by
>>> clk_get_rate(). It would avoid yet another DT binding. If we make the
>>> clock optional, then we won't affect any other platforms. The clock
>>> itself could be a regular fixed clock node.
>>
>> Thinh Nguyen asked to add a dedicated DT property. He explained that
>> clk_get_rate() does not work for PCI hosted dwc3. This is the most
>> complete summary of the discussion:
>>
>>   https://urldefense.com/v3/__https://lore.kernel.org/r/c797e9cb-cae6-c0b6-5714-169c2ad79d32@synopsys.com__;!!A4F2R9G_pg!Nh6rqp_aOd8XIvqELvDRQe5ooZf13UZKwmn9lWcRgdbyMKpTMzL8HasrB1X2Ojvumo8g$ 
> 
> PCI devices can have DT nodes with clock properties too. Or use the 
> VID/PID to infer the frequency. Or use 'clock-frequency' property.
> 
> It boils down to we have lots of standard properties for clocks and 
> clock configuration, so custom properties are a NAK.
> 

Do we have DT node for the PCI device before discovering the device from
PCI bus enumeration? I don't think we can find the clock properties from
its configuration space. For our HAPS devices, we can't use VID/PID to
infer the frequency since our phy and ref clock may change.

Does "clock-frequency" mean ref clock? If so, let's use that?

Thanks,
Thinh