[PATCH 2/3] clk: WARN_ON about to disable a critical clock

[Dirk Behme]

On 03.07.2017 13:53, Lee Jones wrote:
> On Tue, 27 Jun 2017, Dirk Behme wrote:
> 
>> On 11.02.2016 01:43, Michael Turquette wrote:
>>> Quoting Lee Jones (2016-01-18 06:28:50)
>>>> Signed-off-by: Lee Jones <lee.jones at linaro.org>
>>>
>>> Looks good to me.
>>>
>>> Regards,
>>> Mike
>>>
>>>> ---
>>>>    drivers/clk/clk.c | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>>>> index 835cb85..178b364 100644
>>>> --- a/drivers/clk/clk.c
>>>> +++ b/drivers/clk/clk.c
>>>> @@ -575,6 +575,9 @@ static void clk_core_unprepare(struct clk_core *core)
>>>>           if (WARN_ON(core->prepare_count == 0))
>>>>                   return;
>>>> +       if (WARN_ON(core->prepare_count == 1 && core->flags & CLK_IS_CRITICAL))
>>>> +               return;
>>>> +
>>>>           if (--core->prepare_count > 0)
>>>>                   return;
>>>> @@ -680,6 +683,9 @@ static void clk_core_disable(struct clk_core *core)
>>>>           if (WARN_ON(core->enable_count == 0))
>>>>                   return;
>>>> +       if (WARN_ON(core->enable_count == 1 && core->flags & CLK_IS_CRITICAL))
>>>> +               return;
>>>> +
>>>>           if (--core->enable_count > 0)
>>>>                   return;
>>
>>
>> I have a question regarding this patch, which is mainline meanwhile [1]:
>>
>> Having the following clock configuration:
>>
>>                                          |--> child clk '1' (crit)
>> clk source --> parent clk 'A' (crit) -->|
>>                                          |--> child clk '2'
>>
>>
>> Clock '2' might be used, or not. It might be disabled or not. It doesn't
>> matter. Clock '1' is not allowed to be disabled. Therefore its marked as
>> critical.
>>
>> Parent clock 'A' is marked as critical because its not allowed to be
>> disabled, even if the enable_count of all child clocks is 0. To avoid that
>> by disabling parent clock 'A' the child clock '1' is disabled, too, whats
>> not allowed as its marked as critical.
>>
>>
>> Now, child clock '2' is used and enabled & disabled continuously by a (SPI)
>> driver. What is ok. But:
>>
>> Disabling child clock '2' results in the attempt to disable parent clock
>> 'A', too, which has correct enable_count 1 (from enabling the child '2').
>> What results
>>
>> a) in the WARN_ON output
>>
>> and
>>
>> b) enable_count of 'A' never decreases to 0. Being off by one after the
>> WARN_ON
>>
>>
>> It sounds like both is wrong for a configuration like above.
> 
> Clock A still has one user, Clock 1.
> 
> Why is that wrong?


Because clock 1 is not a (Linux kernel clock framework) used clock. Its 
enable count is 0. So from Linux kernel (clock framework) point of view 
clock 1 is unused.

The increase/decrease of enable count of parent clock A is only driven 
by the Linux kernel usage of clock 2.

Best regards

Dirk

>> Opinions or proposal how to fix/change this?
>>
>>
>> Best regards
>>
>> Dirk
>>
>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/clk/clk.c?id=2e20fbf592621b2c2aeddd82e0fa3dad053cce03