Re: [PATCH net-next 03/18] drivers: clk: renesas: r9a07g044-cpg: Add ethernet clock sources

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Biju,

On Mon, Jul 26, 2021 at 1:43 PM Biju Das <biju.das.jz@bp.renesas.com> wrote:
> > Subject: Re: [PATCH net-next 03/18] drivers: clk: renesas: r9a07g044-cpg:
> > Add ethernet clock sources
> > On Thu, Jul 22, 2021 at 4:14 PM Biju Das <biju.das.jz@bp.renesas.com>
> > wrote:
> > > Ethernet reference clock can be sourced from PLL5_2 or PLL6_2. Add
> > > support for ethernet source clock selection using SEL_PLL_6_2 mux.
> > >
> > > Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> > > Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> >
> > Thanks for your patch!
> >
> > > --- a/drivers/clk/renesas/r9a07g044-cpg.c
> > > +++ b/drivers/clk/renesas/r9a07g044-cpg.c
> > > @@ -35,8 +35,10 @@ enum clk_ids {
> > >         CLK_PLL3_DIV4,
> > >         CLK_PLL4,
> > >         CLK_PLL5,
> > > +       CLK_PLL5_2,
> >
> > Why do you need this? We already have CLK_PLL5_DIV2?
>
> As per clock list HP =250 MHz.
>
> With PLL5_DIV2 the frequency, what we get is 3000 x 1/2 = 1500 MHz, which is incorrect
>
> There is some issue with HW manual. It is not clear. I have requested to fix those issue.
>
> Actually PLL5 generates 3 clk outputs (As per page 403 of manual)
>
> FOUTPOSTDIV= 3000
> FOUT3 = 500
> FOUT1PH0 = 1500
>
> To match the clock list document and Figure 8.3 Clock system diagram for HP clock.
> This clock has to be FOUT3.
>
> FOUT3(second PLL5 clock source)* 1/2 =250 MHz(HP clock).
>
> On the HW manual, Divider name for PLL5 is mentioned as PLL_5_2_DIV12 and for PLL6 as PLL6_2_DIV2.
>
> >
> > >         CLK_PLL5_DIV2,
> > >         CLK_PLL6,
> > > +       CLK_PLL6_DIV2,
> > >         CLK_P1_DIV2,
> > >
> > >         /* Module Clocks */
> > > @@ -53,6 +55,9 @@ static const struct clk_div_table dtable_1_32[] = {
> > >         {0, 0},
> > >  };
> > >
> > > +/* Mux clock tables */
> > > +static const char * const sel_pll6_2[] = { ".pll6_2_div2",
> > > +".pll5_2_div2" };
> >
> > ".pll6_div2", ".pll5_div2"
>
> Basically PLL6 generates 2 clock outputs. That is the reason it is termed as PLL6_2 for second clock
> And pll5 generates 3 clock outputs and pll5_2(second clock source) is used for HP.
>
> To match the register definition, I will change this to ".pll6_2_div2" and ".pll5_2_div12". Is it ok?

OK, thanks for the explanation!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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