linux-kernel - Re: [PATCH 0/2] cpufreq/opp: rework regulator initialization

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Date:   Fri, 8 Feb 2019 13:04:18 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Dave Gerlach <d-gerlach@...com>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 0/2] cpufreq/opp: rework regulator initialization

Hi Sudeep,

On 2019-02-08 12:51, Sudeep Holla wrote:
> On Fri, Feb 08, 2019 at 12:47:06PM +0100, Marek Szyprowski wrote:
>> On 2019-02-08 12:00, Sudeep Holla wrote:
>>> On Thu, Feb 07, 2019 at 01:22:25PM +0100, Marek Szyprowski wrote:
>>>> Dear All,
>>>>
>>>> This is a scenario that triggers the above issue:
>>> [...]
>>>> 1. system disables non-boot cpu's at the end of system suspend procedure,
>>>> 2. this in turn deinitializes cpufreq drivers for the disabled cpus,
>>>> 3. early in the system resume procedure all cpus are got back to online
>>>>    state,
>>>> 4. this in turn causes cpufreq to be initialized for the newly onlined
>>>>    cpus,
>>>> 5. cpufreq-dt acquires all its resources (clocks, regulators) during
>>>>    ->init() callback,
>>> This is strictly not just restricted to cpufreq-dt, but to any driver
>>> supporting multiple policies. So we need a generic fix not just
>>> cpufreq-dt specific.
>> Could you point which other driver needs similar fix? Here in cpufreq-dt
>> the problem was caused by using regulator api (indirectly) from
>> ->init(). All other drivers, which have regulators support, are for old,
>> obsolete, uni-processor systems, which don't have the problem of
>> secondary cpu suspend during system suspend/resume cycle.
>>
> scmi_cpufreq for instance. We can fix that in driver my moving to polling
> to get cpufreq_get_rate, but we support both polling and interrupt based.
> We may wait for remote processor interrupt in get_rate.

Frankly, I don't feel I know enough to touch this driver and I don't
think that this can even be fixed in a generic way in the cpufreq core.
Maybe a comment somewhere is needed that ->init() might be called during
early system resume with irqs off and driver is responsible for handling
such case until the proper resume?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland