linux-kernel - Re: [PATCH v2 1/2] PM: enable support for imminent power loss

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Message-ID: <20210726201615.GA2025233@dhcp-10-100-145-180.wdc.com>
Date:   Mon, 26 Jul 2021 13:16:47 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     Pavel Machek <pavel@....cz>
Cc:     shiva.linuxworks@...il.com, rjw@...ysocki.net, len.brown@...el.com,
        linux-pm@...r.kernel.org, axboe@...com, hch@....de,
        sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Shivamurthy Shastri <sshivamurthy@...ron.com>
Subject: Re: [PATCH v2 1/2] PM: enable support for imminent power loss

On Mon, Jul 26, 2021 at 09:41:46PM +0200, Pavel Machek wrote:
> > If the shutdown is pwerformed when the platform is running on the
> > limited backup power supply, some of the devices might not have enough
> > power to perform a clean shutdown.
> > 
> > It is necessary to inform the driver about the limited backup power
> > supply, to allow the driver to decide to perform the minimal required
> > operation for a fast and clean shutdown.
> 
> If you can do shutdown that is fast & clean, why not do it always?

At least for nvme, I don't think this faster shutdown qualifies as
"clean". It's just a little better than removing power without telling
the device. Typical implementations take longer to become ready on their
next power-on following the abrupt shutdown sequence.