linux-kernel - RE: [PATCH] devfreq: Suspend all devices on system shutdown

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Message-ID: <20190128080535epcms1p44636143629448c4e24a6628e87a72bf2@epcms1p4>
Date:   Mon, 28 Jan 2019 17:05:35 +0900
From:   MyungJoo Ham <myungjoo.ham@...sung.com>
To:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>
CC:     Chanwoo Choi <cw00.choi@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Lukasz Luba <l.luba@...tner.samsung.com>,
        Markus Reichl <m.reichl@...etechno.de>
Subject: RE: [PATCH] devfreq: Suspend all devices on system shutdown

>This way devfreq core ensures that all its devices will be set to safe
>operation points before reboot operation. There are board on which some
>aggressive power saving operation points are behind the capabilities of
>the bootloader to properly reset the hardware and boot the board. This
>way one can avoid board crash early after reboot.
>
>Similar pattern is used in CPUfreq subsystem.
>
>Reported-by: Markus Reichl <m.reichl@...etechno.de>
>Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>---

You are invoking ALL devfreq suspend callbacks at shutdown
with this commit.

Can you make it invoke only devices explicitly saying their needs
to handle "SHUTDOWN" event?

For example, we can add a flag at struct devfreq_dev_profile:
"uint32_t requirement"
, where
0x1: need to operate at the initial frequency for suspend
0x2: need to operate at the initial frequency for shutdown
0x4: it forgets its status at resume, reconfigure frequency at resume.
(or reverse 0x1's semantics for the backward compatibility)
...

Cheers,
MyungJoo