Re: [PATCH][RFC] drivers: sh: late disabling of clocks

[Simon Horman <horms@verge.net.au>]

On Thu, Jun 09, 2011 at 06:13:39PM +0900, Magnus Damm wrote:
> From: Magnus Damm <damm@opensource.se>
> 
> This RFC patch kills two birds with one stone:
> 
> 1) Fix existing issue where in-use clocks without software
>    reference are disabled during boot. One example of this
>    is the handling of the Mackerel serial console output.
> 
> 2) Make sure so far unused clocks actually get turned off 

Is access to allow_disable SMP-safe?
In particular, does the the access in clk_late_init()
need to be guarded by clock_lock as calls to __clk_disable() are?

> 
> Signed-off-by: Magnus Damm <damm@opensource.se>
> ---
> 
>  drivers/sh/clk/core.c |   26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> --- 0001/drivers/sh/clk/core.c
> +++ work/drivers/sh/clk/core.c	2011-06-09 14:13:02.000000000 +0900
> @@ -34,6 +34,9 @@ static LIST_HEAD(clock_list);
>  static DEFINE_SPINLOCK(clock_lock);
>  static DEFINE_MUTEX(clock_list_sem);
>  
> +/* clock disable operations are not passed on to hardware during boot */
> +static int allow_disable;
> +
>  void clk_rate_table_build(struct clk *clk,
>  			  struct cpufreq_frequency_table *freq_table,
>  			  int nr_freqs,
> @@ -228,7 +231,7 @@ static void __clk_disable(struct clk *cl
>  		return;
>  
>  	if (!(--clk->usecount)) {
> -		if (likely(clk->ops && clk->ops->disable))
> +		if (likely(allow_disable && clk->ops && clk->ops->disable))
>  			clk->ops->disable(clk);
>  		if (likely(clk->parent))
>  			__clk_disable(clk->parent);
> @@ -747,3 +750,24 @@ err_out:
>  	return err;
>  }
>  late_initcall(clk_debugfs_init);
> +
> +static int __init clk_late_init(void)
> +{
> +	unsigned long flags;
> +	struct clk *clk;
> +
> +	/* from now on allow clock disable operations */
> +	allow_disable = 1;
> +
> +	/* disable all clocks with zero use count */
> +	mutex_lock(&clock_list_sem);
> +	list_for_each_entry(clk, &clock_list, node) {
> +		spin_lock_irqsave(&clock_lock, flags);
> +		if (!clk->usecount && clk->ops && clk->ops->disable)
> +			clk->ops->disable(clk);
> +		spin_unlock_irqrestore(&clock_lock, flags);
> +	}
> +	mutex_unlock(&clock_list_sem);
> +	return 0;
> +}
> +late_initcall(clk_late_init);
> --
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