linux-kernel - Re: [PATCH v4 1/7] clk: kona: allow nested ccu_write

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Date:	Fri, 30 May 2014 16:28:22 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Alex Elder <elder@...aro.org>, mporter@...aro.org,
	bcm@...thebug.org
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/7] clk: kona: allow nested ccu_write_enable() requests

Quoting Alex Elder (2014-05-30 13:53:02)
> Use a counter rather than a Boolean to track whether write access to
> a CCU has been enabled or not.  This will allow more than one of
> these requests to be nested.
> 
> Note that __ccu_write_enable() and __ccu_write_disable() calls all
> come in pairs, and they are always surrounded immediately by calls
> to ccu_lock() and ccu_unlock().
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
>  drivers/clk/bcm/clk-kona.c | 14 ++++----------
>  drivers/clk/bcm/clk-kona.h |  2 +-
>  2 files changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/clk/bcm/clk-kona.c b/drivers/clk/bcm/clk-kona.c
> index 95af2e6..ee8e988 100644
> --- a/drivers/clk/bcm/clk-kona.c
> +++ b/drivers/clk/bcm/clk-kona.c
> @@ -170,13 +170,8 @@ static inline void ccu_unlock(struct ccu_data *ccu, unsigned long flags)
>   */
>  static inline void __ccu_write_enable(struct ccu_data *ccu)

Per Documentation/CodingStyle, chapter 15, "the inline disease", it
might be best to not inline these functions.

>  {
> -       if (ccu->write_enabled) {
> -               pr_err("%s: access already enabled for %s\n", __func__,
> -                       ccu->name);
> -               return;
> -       }
> -       ccu->write_enabled = true;
> -       __ccu_write(ccu, 0, CCU_ACCESS_PASSWORD | 1);
> +       if (!ccu->write_enabled++)
> +               __ccu_write(ccu, 0, CCU_ACCESS_PASSWORD | 1);
>  }
>  
>  static inline void __ccu_write_disable(struct ccu_data *ccu)
> @@ -186,9 +181,8 @@ static inline void __ccu_write_disable(struct ccu_data *ccu)
>                         ccu->name);
>                 return;
>         }
> -
> -       __ccu_write(ccu, 0, CCU_ACCESS_PASSWORD);
> -       ccu->write_enabled = false;
> +       if (!--ccu->write_enabled)
> +               __ccu_write(ccu, 0, CCU_ACCESS_PASSWORD);

What happens if calls to __ccu_write_enable and __ccu_write_disable are
unbalanced? It would be better to catch that case and throw a WARN:

	if (WARN_ON(ccu->write_enabled == 0))
		return;

	if (--ccu->write_enabled > 0)
		return;

	__ccu_write(ccu, 0, CCU_ACCESS_PASSWORD);

>  }
>  
>  /*
> diff --git a/drivers/clk/bcm/clk-kona.h b/drivers/clk/bcm/clk-kona.h
> index 2537b30..e9a8466 100644
> --- a/drivers/clk/bcm/clk-kona.h
> +++ b/drivers/clk/bcm/clk-kona.h
> @@ -478,7 +478,7 @@ struct ccu_policy {
>  struct ccu_data {
>         void __iomem *base;     /* base of mapped address space */
>         spinlock_t lock;        /* serialization lock */
> -       bool write_enabled;     /* write access is currently enabled */
> +       u32 write_enabled;      /* write access enable count */

Why u32? An unsigned int will do just nicely here.

Regards,
Mike

>         struct ccu_policy policy;
>         struct list_head links; /* for ccu_list */
>         struct device_node *node;
> -- 
> 1.9.1
> 
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