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SubjectRe: [RFC PATCH V1 2/2] clk: add lock for clk_core_is_enabled
On 12/22, Dong Aisheng wrote:
> According to design doc, .is_enabled should be protected by enable lock.
> Then users don't have to protect it against enable/disable operation
> in clock drivers.
>
> See: Documentation/clk.txt
> "The enable lock is a spinlock and is held across calls to the .enable,
> .disable and .is_enabled operations."
>
> Cc: Stephen Boyd <sboyd@codeaurora.org>
> Cc: Michael Turquette <mturquette@baylibre.com>
> Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
> ---
> drivers/clk/clk.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index e24968f..d6e2d5c 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -198,14 +198,19 @@ static bool clk_core_is_prepared(struct clk_core *core)
>
> static bool clk_core_is_enabled(struct clk_core *core)
> {
> + unsigned long flags;
> bool ret = false;
>
> + flags = clk_enable_lock();
> +
> /*
> * .is_enabled is only mandatory for clocks that gate
> * fall back to software usage counter if .is_enabled is missing
> */
> - if (!core->ops->is_enabled)
> + if (!core->ops->is_enabled) {
> + clk_enable_unlock(flags);
> return core->enable_count;
> + }
>
> /*
> * Check if clock controller's device is runtime active before
> @@ -230,6 +235,8 @@ static bool clk_core_is_enabled(struct clk_core *core)
> if (core->dev)
> pm_runtime_put(core->dev);
>
> + clk_enable_unlock(flags);
> +
> return ret;
> }

It doesn't really make any sense to hold the enable lock inside
the clk_core_is_enabled() function, unless you want to do
something else with the information of the enable state with that
lock held. Otherwise, seeing if a clk is enabled is a one-shot
read of the enabled state, which could just as easily change
after the function returns because the lock is released.

We should update the documentation.

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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