[PATCH v3 05/11] clk: k210: Move the clint clock to under aclk

[Sean Anderson <seanga2@gmail.com>]

On 4/8/21 10:58 PM, Damien Le Moal wrote:
> On 2021/04/09 11:54, Damien Le Moal wrote:
>> On 2021/04/09 11:13, Sean Anderson wrote:
>>> No other (real) clocks have the cpu clock as their parent; instead they are
>>> children of aclk. Move the clint clock under aclk to match them.
>>>
>>> Signed-off-by: Sean Anderson <seanga2@gmail.com>
>>> ---
>>>
>>> (no changes since v2)
>>>
>>> Changes in v2:
>>> - New
>>>
>>>   drivers/clk/kendryte/clk.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/clk/kendryte/clk.c b/drivers/clk/kendryte/clk.c
>>> index ab86533bb4..5091f07eb0 100644
>>> --- a/drivers/clk/kendryte/clk.c
>>> +++ b/drivers/clk/kendryte/clk.c
>>> @@ -643,7 +643,7 @@ static int k210_clk_probe(struct udevice *dev)
>>>   
>>>   	/* The MTIME register in CLINT runs at one 50th the CPU clock speed */
>>>   	clk_dm(K210_CLK_CLINT,
>>> -	       clk_register_fixed_factor(NULL, "clint", "cpu", 0, 1, 50));
>>> +	       clk_register_fixed_factor(NULL, "clint", "aclk", 0, 1, 50));
>>>   
>>>   	return 0;
>>>   }
>>>
>>
>> Looks good, but representing this clock is in fact useless, at least in Linux,
>> since the clint driver does not use it directly and derives its rate from
>> riscv_timebase which is set from the timebase-frequency DT property.
>>
>> Not sure how u-boot handles that though. Since your code allows changing the
>> PLLs frequency, the timebase-frequency property may end up being buggy if it is
>> not changed too.
> 
> Actually, thinking about this some more, the clint DT node should have an
> optional clock entry and use that clock rate to set riscv_timebase if the clock
> entry is present. riscv_timebase can be set using timebase-frequency DT property
> if the clock is not set.

This is how it is done in U-Boot. See timer_pre_probe and
timer_timebase_fallback for the mechanism.

--Sean