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

[Sean Anderson]

On 12/7/20 5:14 AM, Damien Le Moal wrote:
> On 2020/12/07 19:06, Geert Uytterhoeven wrote:
>> Hi Damien,
>>
>> On Mon, Dec 7, 2020 at 10:55 AM Damien Le Moal <Damien.LeMoal at 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 at 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?
> 
> I am not 100% sure if this oscillator is part of the SoC or if it is an external
> input to it. Probably not. Hard to tell by just looking at the boards.

It's an external crystal. For example, it is U6 on the maix bit. This is
why I put it as a separate clock instead of including it with the rest.

--Sean

> I have
> the boards drawings though, so  I will check. The frequency seems to be fixed by
> hardware: frequencies of the PLLs can be changed to change the CPU frequency,
> but the Kendryte SDK does not point to any way allowing changing the base
> frequency of the oscillator> 
>> 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 at 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
>>
> 
>