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SubjectRe: [RFC] memory: exynos5422-dmc: Document mutex scope
Date
Hi Krzysztof,

On 7/24/20 7:08 PM, Krzysztof Kozlowski wrote:
> Document scope of the mutex used by driver.
>
> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
>
> ---
>
> It seems mutex was introduced to protect:
> 1. setting actual frequency/voltage,
> 2. dmc->curr_rate (in exynos5_dmc_get_cur_freq()).
>
> However dmc->curr_rate in exynos5_dmc_get_status() is not protected. Is
> it a bug?

The callback get_dev_status() from devfreq->profile, which here is the
exynos5_dmc_get_status() should be already called with devfreq->lock
mutex hold, like e.g from simple_ondemand governor or directly
using update_devfreq exported function:
update_devfreq()
->get_target_freq()
devfreq_update_stats()
df->profile->get_dev_status()

The dmc->curr_rate is also used from sysfs interface from devfreq.
The local dmc lock serializes also this use case (when the HW freq
has changed but not set yet into curr_rate.


> ---
> drivers/memory/samsung/exynos5422-dmc.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/memory/samsung/exynos5422-dmc.c b/drivers/memory/samsung/exynos5422-dmc.c
> index 93e9c2429c0d..0388066a7d96 100644
> --- a/drivers/memory/samsung/exynos5422-dmc.c
> +++ b/drivers/memory/samsung/exynos5422-dmc.c
> @@ -114,6 +114,7 @@ struct exynos5_dmc {
> void __iomem *base_drexi0;
> void __iomem *base_drexi1;
> struct regmap *clk_regmap;
> + /* Protects curr_rate and frequency/voltage setting section */
> struct mutex lock;
> unsigned long curr_rate;
> unsigned long curr_volt;
>

I assume this missing comment for the lock was required by some scripts.
In this case LGTM:

Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>

Regards,
Lukasz

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