Re: [PATCH 1/2] clk: Fix the CLK_IGNORE_UNUSED failure issue

[Chuan Liu <chuan.liu@amlogic.com>]

Hi Jerome:

     Thanks for your suggestion.


On 9/30/2024 8:27 PM, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
>
> On Sun 29 Sep 2024 at 14:10, Chuan Liu via B4 Relay <devnull+chuan.liu.amlogic.com@kernel.org> wrote:
>
>> From: Chuan Liu <chuan.liu@amlogic.com>
>>
>> When the clk_disable_unused_subtree() function disables an unused clock,
>> if CLK_OPS_PARENT_ENABLE is configured on the clock,
>> clk_core_prepare_enable() and clk_core_disable_unprepare() are called
>> directly, and these two functions do not determine CLK_IGNORE_UNUSED,
>> This causes the clock to be disabled even if CLK_IGNORE_UNUSED is
>> configured when clk_core_disable_unprepare() is called.
>>
>> Two new functions clk_disable_unprepare_unused() and
>> clk_prepare_enable_unused() are added to resolve the preceding
>> situation. The CLK_IGNORE_UNUSED judgment logic is added to these two
>> functions. To prevent clock configuration CLK_IGNORE_UNUSED from
>> possible failure.
>>
>> Change-Id: I56943e17b86436254f07d9b8cdbc35599328d519
>> Signed-off-by: Chuan Liu <chuan.liu@amlogic.com>
>> ---
>>   drivers/clk/clk.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 65 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>> index 285ed1ad8a37..5d3316699b57 100644
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -94,6 +94,7 @@ struct clk_core {
>>        struct hlist_node       debug_node;
>>   #endif
>>        struct kref             ref;
>> +     bool                    ignore_enabled;
>>   };
>>
>>   #define CREATE_TRACE_POINTS
>> @@ -1479,6 +1480,68 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
>>        }
>>   }
>>
>> +static void __init clk_disable_unprepare_unused(struct clk_core *core)
>> +{
>> +     unsigned long flags;
>> +
>> +     lockdep_assert_held(&prepare_lock);
>> +
>> +     if (!core)
>> +             return;
>> +
>> +     if ((core->enable_count == 0) && core->ops->disable &&
>> +         !core->ignore_enabled) {
>> +             flags = clk_enable_lock();
> Used core->enable_count without taking the lock

My understanding is that adding a spinlock here is to ensure that
the disabling of the clock can be completed without interference.

>
>> +             core->ops->disable(core->hw);
> If the there is any CLK_IS_CRITICAL in the path, it is game over.
> You've basically disregarded all the other CCF flags which are equally
> important to the ones you are dealing with.

if clock is CLK_IS_CRITICAL then its enable_count > 0 does not go into
the 'if'.

>
>> +             clk_enable_unlock(flags);
>> +     }
>> +
>> +     if ((core->prepare_count == 0) && core->ops->unprepare &&
>> +         !core->ignore_enabled)
>> +             core->ops->unprepare(core->hw);
>> +
>> +     core->ignore_enabled = false;
>> +
>> +     clk_disable_unprepare_unused(core->parent);
> Here you are disabling the parent of any CLK_IGNORE_UNUSED clock.
> IMO, the problem is not solved. It just shifted.

Yes, it does not take into account the situation where its parent is
disabled without configuring CLK_IGNORE_UNUSED.

>
>> +}
>> +
>> +static int __init clk_prepare_enable_unused(struct clk_core *core)
>> +{
>> +     int ret = 0;
>> +     unsigned long flags;
>> +
>> +     lockdep_assert_held(&prepare_lock);
>> +
>> +     if (!core)
>> +             return 0;
>> +
>> +     ret = clk_prepare_enable_unused(core->parent);
>> +     if (ret)
>> +             return ret;
> That's adding another recursion in CCF, something Stephen would like to remove

This patch is meant to throw out an idea and bring attention to the
problem that was discovered.

>> +
>> +     if ((core->flags & CLK_IGNORE_UNUSED) && clk_core_is_enabled(core))
>> +             core->ignore_enabled = true;
>> +
>> +     if ((core->prepare_count == 0) && core->ops->prepare) {
>> +             ret = core->ops->prepare(core->hw);
>> +             if (ret)
>> +                     goto disable_unprepare;
>> +     }
>> +
>> +     if ((core->enable_count == 0) && core->ops->enable) {
>> +             flags = clk_enable_lock();
>> +             ret = core->ops->enable(core->hw);
>> +             clk_enable_unlock(flags);
>> +             if (ret)
>> +                     goto disable_unprepare;
>> +     }
>> +
>> +     return 0;
>> +disable_unprepare:
>> +     clk_disable_unprepare_unused(core->parent);
>> +     return ret;
>> +}
>> +
>>   static void __init clk_disable_unused_subtree(struct clk_core *core)
>>   {
>>        struct clk_core *child;
>> @@ -1490,7 +1553,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>>                clk_disable_unused_subtree(child);
>>
>>        if (core->flags & CLK_OPS_PARENT_ENABLE)
>> -             clk_core_prepare_enable(core->parent);
>> +             clk_prepare_enable_unused(core->parent);
>>
>>        flags = clk_enable_lock();
>>
>> @@ -1517,7 +1580,7 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>>   unlock_out:
>>        clk_enable_unlock(flags);
>>        if (core->flags & CLK_OPS_PARENT_ENABLE)
>> -             clk_core_disable_unprepare(core->parent);
>> +             clk_disable_unprepare_unused(core->parent);
>>   }
>>
>>   static bool clk_ignore_unused __initdata;
> --
> Jerome