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SubjectRe: [PATCH 1/1] arm: mxc: utilise usecount field in clock operations
On 04/22/2010 02:30 PM, Amit Kucheria wrote:
> From: Amit Kucheria<amit.kucheria@canonical.com>
>
> This patch fixes the clock refcounting when reparenting is used.
>
> Sascha just pointed out a good explanation of refcounting here:
> http://www.spinics.net/lists/arm-kernel/msg85879.html
>
> Signed-off-by: Amit Kucheria<amit.kucheria@canonical.com>
> ---
> arch/arm/plat-mxc/clock.c | 34 ++++++++++++++++++++++------------
> 1 files changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/plat-mxc/clock.c b/arch/arm/plat-mxc/clock.c
> index 323ff8c..14781cc 100644
> --- a/arch/arm/plat-mxc/clock.c
> +++ b/arch/arm/plat-mxc/clock.c
> @@ -50,15 +50,16 @@ static DEFINE_MUTEX(clocks_mutex);
>
> static void __clk_disable(struct clk *clk)
> {
> - if (clk == NULL || IS_ERR(clk))
> + WARN_ON(!clk->usecount);
> + if (clk == NULL || IS_ERR(clk) || !clk->usecount)
> return;
>

The clk==NULL check seem superfluous if WARN_ON(!clk->usecount) has
already dereferenced clk (and possibly crashed). You might need two
statements if its likely that clk could be NULL.

> - __clk_disable(clk->parent);
> - __clk_disable(clk->secondary);
> -
> - WARN_ON(!clk->usecount);
> - if (!(--clk->usecount)&& clk->disable)
> - clk->disable(clk);
> + if (!(--clk->usecount)) {
> + if (clk->disable)
> + clk->disable(clk);
> + __clk_disable(clk->parent);
> + __clk_disable(clk->secondary);
> + }
> }
>
> static int __clk_enable(struct clk *clk)
> @@ -66,12 +67,13 @@ static int __clk_enable(struct clk *clk)
> if (clk == NULL || IS_ERR(clk))
> return -EINVAL;
>
> - __clk_enable(clk->parent);
> - __clk_enable(clk->secondary);
> -
> - if (clk->usecount++ == 0&& clk->enable)
> - clk->enable(clk);
> + if (clk->usecount++ == 0) {
> + __clk_enable(clk->parent);
> + __clk_enable(clk->secondary);
>
> + if (clk->enable)
> + clk->enable(clk);
> + }
> return 0;
> }
>
> @@ -160,17 +162,25 @@ EXPORT_SYMBOL(clk_set_rate);
> int clk_set_parent(struct clk *clk, struct clk *parent)
> {
> int ret = -EINVAL;
> + struct clk *prev_parent = clk->parent;
>
> if (clk == NULL || IS_ERR(clk) || parent == NULL ||
> IS_ERR(parent) || clk->set_parent == NULL)
> return ret;
>
> + if (clk->usecount != 0)
> + clk_enable(parent);
> +
> mutex_lock(&clocks_mutex);
> ret = clk->set_parent(clk, parent);
> if (ret == 0)
> clk->parent = parent;
> +
> mutex_unlock(&clocks_mutex);
>
> + if (clk->usecount != 0)
> + clk_disable(prev_parent);
> +
> return ret;
> }
> EXPORT_SYMBOL(clk_set_parent);


--
Tim Gardner tim.gardner@canonical.com


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