Re: [PATCH v4 11/21] riscv: Add Canaan Kendryte K210 clock driver

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

Hi Damien,

On Mon, Dec 7, 2020 at 10:55 AM Damien Le Moal <Damien.LeMoal@wdc.com> wrote:
> On 2020/12/07 17:44, Geert Uytterhoeven wrote:
> > On Mon, Dec 7, 2020 at 4:52 AM Damien Le Moal <Damien.LeMoal@wdc.com> wrote:
> >> I prepared a v5 series addressing your comments (and other comments).
> >> I will post that later today after some more tests.
> >
> > Thanks, already looking at k210-sysctl-v18...
> >
> >> On Fri, 2020-12-04 at 22:19 -0800, Stephen Boyd wrote:
> >>>> --- /dev/null
> >>>> +++ b/drivers/clk/clk-k210.c
> >
> >>>> +       in0_clk = of_clk_get(np, 0);
> >>>> +       if (IS_ERR(in0_clk)) {
> >>>> +               pr_warn("%pOFP: in0 oscillator not found\n", np);
> >>>> +               hws[K210_CLK_IN0] =
> >>>> +                       clk_hw_register_fixed_rate(NULL, "in0", NULL,
> >>>> +                                                  0, K210_IN0_RATE);
> >>>> +       } else {
> >>>> +               hws[K210_CLK_IN0] = __clk_get_hw(in0_clk);
> >>>> +       }
> >>>> +       if (IS_ERR(hws[K210_CLK_IN0])) {
> >>>> +               pr_err("%pOFP: failed to get base oscillator\n", np);
> >>>> +               goto err;
> >>>> +       }
> >>>> +
> >>>> +       in0 = clk_hw_get_name(hws[K210_CLK_IN0]);
> >>>> +       aclk_parents[0] = in0;
> >>>> +       pll_parents[0] = in0;
> >>>> +       mux_parents[0] = in0;
> >>>
> >>> Can we use the new way of specifying clk parents so that we don't have
> >>> to use __clk_get_hw(), of_clk_get(), and clk_hw_get_name()? Hopefully
> >>> the core can handl that all instead of this driver.
> >>
> >> I removed all this by adding:
> >>
> >> clock-output-names = "in0";
> >>
> >> to the DT fixed-rate oscillator clock node (and documented that too). Doing so,
> >> clk_hw_get_name(), __clk_get_hw() and of_clk_get() are not needed anymore and
> >> the parents clock names arrays do not need run-time update.
> >
> > "clock-output-names" is deprecated for clocks with a single output:
> > the clock name will be taken from the node name.
>
> Arg. I missed that.
>
> > However, relying on a clock name like this is fragile.
> > Instead, your driver should use the phandle from the clocks property,
> > using of_clk_get_by_name() or of_clk_get().
>
> That is what all versions before V5 used. But Stephen mentioned that the driver
> should not, if possible, use of_clk_get()/__clk_get_name(). Hence the change.
> Easy to revert back.
>
> > Stephen: I'm a bit puzzled, as you suggest _not_ using of_clk_get()?
>
> Another solution to this would be to simply remove the fixed-rate clock node
> from the DT and have the k210 clock driver unconditionally create that clock
> (that is one line !). That actually may be even more simple than the previous
> version, albeit at the cost of having the DT not being a perfect description of
> the hardware. I am fine with that though.
>
> Thoughts ?

If there's an external crystal, DT should describe it.
Does the K210 support different crystal frequencies?

Anyway, I'm very interested in what the (new) proper way of handling this
is...

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