linux-kernel - Re: [PATCH 58/78] media: exynos-gsc: use pm_runtime_resume_and

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Message-ID: <01a14e06-b7f2-7246-ad12-4a13a96622a0@kernel.org>
Date:   Wed, 28 Apr 2021 10:27:30 +0200
From:   Sylwester Nawrocki <snawrocki@...nel.org>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        Sylwester Nawrocki <s.nawrocki@...sung.com>
Subject: Re: [PATCH 58/78] media: exynos-gsc: use pm_runtime_resume_and_get()

On 28.04.2021 09:17, Mauro Carvalho Chehab wrote:
> Em Wed, 28 Apr 2021 09:13:02 +0200
> Mauro Carvalho Chehab <mchehab+huawei@...nel.org> escreveu:
> 
>> Em Tue, 27 Apr 2021 13:50:44 +0200
>> Sylwester Nawrocki <s.nawrocki@...sung.com> escreveu:
>>
>>> On 27.04.2021 11:42, Mauro Carvalho Chehab wrote:

>>> I think if the device is brought into suspended state (e.g. by
>>> disabling clocks as above) the pm_runtime_set_suspended() call
>>> should be there. IOW a following sequence:
>>>
>>> 	pm_runtime_disable(dev);
>>> 	if (!pm_runtime_status_suspended(dev))
>>> 		/* put device into suspended state (disable clocks,
>>> 		  voltage regulators, assert GPIOs, etc. */
>>> 	pm_runtime_set_suspended(dev);
>>
>> Not sure if this would work, as the clock framework would try
>> to do things like calling clk_pm_runtime_put().

It's done in multiple drivers this way. clk_pm_runtime_put() operates
on different device - the clock supplier, not the consumer device.
We just need to disable runtime PM for GSC as the last step, to avoid
any possible v4l2 m2m device_run() call with runtime PM disabled.

>> Perhaps an alternative would be to just return an error if it
>> can't resume PM runtime, e. g.:
[...]
> Nah, forget about that. Despite the platform driver having a return code,
> support for it bogus:

Yes, we can't really stop remove() from driver level so as much complete
resource release is being done as possible.


Regards,
Sylwester