From: Krzysztof Kozlowski <krzk@kernel.org>
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: Kukjin Kim <kgene@kernel.org>,
linux-pm@vger.kernel.org,
"linux-samsung-soc@vger.kernel.org"
<linux-samsung-soc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC] memory: exynos5422-dmc: Document mutex scope
Date: Sun, 9 Aug 2020 11:12:20 +0200 [thread overview]
Message-ID: <CAJKOXPe3OeKFhmtbF4OZup_ii_rxRHTaSK5BT-3T6ijqUukqtg@mail.gmail.com> (raw)
In-Reply-To: <3522860a-8158-6e71-9d65-01d0e0c15f0d@arm.com>
On Tue, Aug 04, 2020 at 11:40:07AM +0100, Lukasz Luba wrote:
> 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.
These are different locks. You cannot protect dmc->curr_rate with
devfreq->lock in one place and dmc-lock in other place. This won't
protect it.
> > ---
> > 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>
Such comments are always useful. It is also pointed by strict
checkpatch:
CHECK: struct mutex definition without comment
Best regards,
Krzysztof
next prev parent reply other threads:[~2020-08-09 9:12 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-24 18:08 [RFC] memory: exynos5422-dmc: Document mutex scope Krzysztof Kozlowski
2020-08-04 10:40 ` Lukasz Luba
2020-08-09 9:12 ` Krzysztof Kozlowski [this message]
2020-08-11 9:27 ` Lukasz Luba
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