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

[Rob Herring]

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 at 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://lore.kernel.org/r/c797e9cb-cae6-c0b6-5714-169c2ad79d32@synopsys.com

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.

Rob