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

[Jerome Brunet <jbrunet@baylibre.com>]

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

> +		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.

> +		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.

> +}
> +
> +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

> +
> +	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