Re: [PATCH v5 02/05] clk: shmobile: Add Renesas R-Car Gen3 CPG support

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Tuesday 01 September 2015 13:36:28 Geert Uytterhoeven wrote:
> On Tue, Sep 1, 2015 at 12:59 PM, Magnus Damm <magnus.damm@gmail.com> wrote:
> >>> +/*
> >>> + *   MD              EXTAL           PLL0    PLL1    PLL2    PLL3   
> >>> PLL4
> >>> + * 14 13 19 17       (MHz)           *1      *1      *1
> >>> + *-------------------------------------------------------------------
> >>> + * 0  0  0  0        16.66 x 1       x180/2  x192/2  x144/2  x192   
> >>> x144
> >>> + * 0  0  0  1        16.66 x 1       x180/2  x192/2  x144/2  x128   
> >>> x144
> >>> + * 0  0  1  0        Prohibited setting
> >>> + * 0  0  1  1        16.66 x 1       x180/2  x192/2  x144/2  x192   
> >>> x144
> >>> + * 0  1  0  0        20    x 1       x150/2  x156/2  x120/2  x156   
> >>> x120
> >>> + * 0  1  0  1        20    x 1       x150/2  x156/2  x120/2  x106   
> >>> x120
> >>> + * 0  1  1  0        Prohibited setting
> >>> + * 0  1  1  1        20    x 1       x150/2  x156/2  x120/2  x156   
> >>> x120
> >>> + * 1  0  0  0        25    x 1       x120/2  x128/2  x96/2   x128   
> >>> x96
> >>> + * 1  0  0  1        25    x 1       x120/2  x128/2  x96/2   x84    
> >>> x96
> >>> + * 1  0  1  0        Prohibited setting
> >>> + * 1  0  1  1        25    x 1       x120/2  x128/2  x96/2   x128   
> >>> x96
> >>> + * 1  1  0  0        33.33 / 2       x180/2  x192/2  x144/2  x192   
> >>> x144
> >>> + * 1  1  0  1        33.33 / 2       x180/2  x192/2  x144/2  x128   
> >>> x144
> >>> + * 1  1  1  0        Prohibited setting
> >>> + * 1  1  1  1        33.33 / 2       x180/2  x192/2  x144/2  x192   
> >>> x144
> >>> + *
> >>> + * *1 : datasheet indicates VCO output (PLLx = VCO/2)
> >> 
> >> As explained in a separate e-mail there's a few clocks on R8A7795 that
> >> derive directly from PLL1 VCO. I thus wonder whether we shouldn't expose
> >> the PLL1 clock as the VCO output and create VCO/2 using a fixed factor
> >> clock in DT.
> >
> > Do you think that would reduce complexity or simplify the code? If so
> > I think we should do it. Otherwise I think it makes sense to simply
> > follow the data sheet.
> 
> It would avoid having to apply a multiplier of two to the RPC clock.

And it would match the hardware clock tree topology. Applying a multiplier to 
the RPC clock is a hack I can live with though, so I'll let you decide which 
option is best, but in general matching the hardware seems a good idea to me.

-- 
Regards,

Laurent Pinchart