Re: [RFC] memory: exynos5422-dmc: Document mutex scope

[Lukasz Luba]

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@xxxxxxxxxx>
> > >
> > > ---
> > >
> > > 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