Re: [PATCH v7 3/5] clk: Supply the critical clock {init, enable, disable} framework

[Maxime Ripard]

On Wed, Jul 22, 2015 at 02:04:13PM +0100, Lee Jones wrote:
> These new API calls will firstly provide a mechanisms to tag a clock as
> critical and secondly allow any knowledgeable driver to (un)gate clocks,
> even if they are marked as critical.
> 
> Suggested-by: Maxime Ripard <maxime.rip...@free-electrons.com>
> Signed-off-by: Lee Jones <lee.jo...@linaro.org>
> ---
>  drivers/clk/clk.c            | 45 
> ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/clk-provider.h |  2 ++
>  include/linux/clk.h          | 30 +++++++++++++++++++++++++++++
>  3 files changed, 77 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 61c3fc5..486b1da 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -46,6 +46,21 @@ static struct clk_core *clk_core_lookup(const char *name);
>  
>  /***    private data structures    ***/
>  
> +/**
> + * struct critical - Provides 'play' over critical clocks.  A clock can be
> + *                   marked as critical, meaning that it should not be
> + *                   disabled.  However, if a driver which is aware of the
> + *                   critical behaviour wants to control it, it can do so
> + *                   using clk_enable_critical() and clk_disable_critical().
> + *
> + * @enabled  Is clock critical?  Once set, doesn't change
> + * @leave_on Self explanatory.  Can be disabled by knowledgeable drivers
> + */
> +struct critical {
> +     bool enabled;
> +     bool leave_on;
> +};
> +
>  struct clk_core {
>       const char              *name;
>       const struct clk_ops    *ops;
> @@ -75,6 +90,7 @@ struct clk_core {
>       struct dentry           *dentry;
>  #endif
>       struct kref             ref;
> +     struct critical         critical;
>  };
>  
>  struct clk {
> @@ -995,6 +1011,10 @@ static void clk_core_disable(struct clk_core *clk)
>       if (WARN_ON(clk->enable_count == 0))
>               return;
>  
> +     /* Refuse to turn off a critical clock */
> +     if (clk->enable_count == 1 && clk->critical.leave_on)
> +             return;
> +

I think it should be handled by a separate counting. Otherwise, if you
have two users that marked the clock as critical, and then one of them
disable it...

>       if (--clk->enable_count > 0)
>               return;
>  
> @@ -1037,6 +1057,13 @@ void clk_disable(struct clk *clk)
>  }
>  EXPORT_SYMBOL_GPL(clk_disable);
>  
> +void clk_disable_critical(struct clk *clk)
> +{
> +     clk->core->critical.leave_on = false;

.. you just lost the fact that it was critical in the first place.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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