linux-kernel - Re: [PATCH 2/3] clk: WARN_ON about to disable a critical clock

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Date:   Tue, 27 Jun 2017 13:16:01 +0200
From:   Dirk Behme <dirk.behme@...bosch.com>
To:     Michael Turquette <mturquette@...libre.com>,
        Lee Jones <lee.jones@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     <kernel@...inux.com>, <s.hauer@...gutronix.de>,
        <sboyd@...eaurora.org>, <geert@...ux-m68k.org>,
        <maxime.ripard@...e-electrons.com>, <maxime.coquelin@...com>
Subject: Re: [PATCH 2/3] clk: WARN_ON about to disable a critical clock

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@...aro.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.

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