From: Lukasz Luba <lukasz.luba@arm.com>
To: Krzysztof Kozlowski <krzk@kernel.org>
Cc: "linux-samsung-soc@vger.kernel.org"
<linux-samsung-soc@vger.kernel.org>,
Kukjin Kim <kgene@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org
Subject: Re: [RFC] memory: exynos5422-dmc: Document mutex scope
Date: Tue, 11 Aug 2020 10:27:31 +0100 [thread overview]
Message-ID: <6db3a6a4-fe56-d448-14c7-ed43de809acb@arm.com> (raw)
In-Reply-To: <CAJKOXPe3OeKFhmtbF4OZup_ii_rxRHTaSK5BT-3T6ijqUukqtg@mail.gmail.com>
On 8/9/20 10:12 AM, Krzysztof Kozlowski wrote:
> 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.
There are different paths that framework goes and mainly they are
protected by the df->lock.
But I tend to agree, I will send a patch which adds some locking.
Regards,
Lukasz
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prev parent reply other threads:[~2020-08-11 9:29 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
2020-08-11 9:27 ` Lukasz Luba [this message]
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