Hi Geert-san,
> From: Geert Uytterhoeven
> Sent: Thursday, May 18, 2017 9:43 PM
>
> Hi Shimoda-san,
>
> On Thu, May 18, 2017 at 2:19 PM, Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> >> From: Geert Uytterhoeven
> >> Sent: Thursday, May 18, 2017 8:41 PM
> >> On Thu, May 18, 2017 at 1:13 PM, Yoshihiro Shimoda
> >> <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> >> >> >> +- reg: offset and length of the partial USB 3.0 Host PHY register block.
> >> >> >> +- #phy-cells: see phy-bindings.txt in the same directory, must be <0>.
> >> >> >
> >> >> > I think we should add "clocks" property as required.
> >> >> >
> >> >> >> +Optional properties:
> >> >> >
> >> >> > You should add "renesas,use-on-chip-clk" here.
> >> >> > And, the name of "use-on-chip-clk" is not good to me.
> >> >> > FYI, my developing patch names "renesas,usb-extal".
> >
> > I'm sorry for this. I missed description "on-chip clock source is supplied though
> > USB_EXTAL/USB_XTAL" in the manual. So, this "renesas,use-on-chip-clk" is reasonable.
> >
> >> >> Can this be decided at runtime, e.g. by looking at the rates of the clocks
> >> >> to see which one is available/best suited?
> >> >
> >> > According to the HW manual, this module cannot see which one is available/best suited.
> >> > So, I don't think this can be decided at runtime.
> >>
> >> I mean, can't Linux look at the rates of the two clocks, and if one is zero,
> >> use the other?
> >
> > I still misunderstand your question though, but software cannot look at the rates
> > of USB3S0_CLK_P/USB3S0_CLK_M and USB_EXTAL/XTAL because the HW doesn't have registers
> > for indicating the rates.
>
> If we have "clocks" properties, as you suggested, both clocks will have to
> be described in DT. Hence Linux will create clock objects for them, and the
> USB PHY driver can call clk_get_rate() on those objects.
>
> If no clock is connected to USB3S0_CLK_P/USB3S0_CLK_M, a dummy clock
> with zero rate should be described in DT.
>
> Cfr. the existing clocks with "clock-frequency = <0>" in r8a7795.dtsi.
Thank you for the detailed explanation!
I understood it. I will try to use such properties.
Best regards,
Yoshihiro Shimoda
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
