linux-kernel - Re: [PATCH v1 0/3] introduce priority-based shutdown support

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Message-ID: <20231124163234.GC819414@pengutronix.de>
Date:   Fri, 24 Nov 2023 17:32:34 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mark Brown <broonie@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org,
        linux-pm@...r.kernel.org,
        Søren Andersen <san@...v.dk>
Subject: Re: [PATCH v1 0/3] introduce priority-based shutdown support

On Fri, Nov 24, 2023 at 03:56:19PM +0000, Greg Kroah-Hartman wrote:
> On Fri, Nov 24, 2023 at 03:49:46PM +0000, Mark Brown wrote:
> > On Fri, Nov 24, 2023 at 03:27:48PM +0000, Greg Kroah-Hartman wrote:
> > > On Fri, Nov 24, 2023 at 03:21:40PM +0000, Mark Brown wrote:
> > 
> > > > This came out of some discussions about trying to handle emergency power
> > > > failure notifications.
> > 
> > > I'm sorry, but I don't know what that means.  Are you saying that the
> > > kernel is now going to try to provide a hard guarantee that some devices
> > > are going to be shut down in X number of seconds when asked?  If so, why
> > > not do this in userspace?
> > 
> > No, it was initially (or when I initially saw it anyway) handling of
> > notifications from regulators that they're in trouble and we have some
> > small amount of time to do anything we might want to do about it before
> > we expire.
> 
> So we are going to guarantee a "time" in which we are going to do
> something?  Again, if that's required, why not do it in userspace using
> a RT kernel?

For the HW in question I have only 100ms time before power loss. By
doing it over use space some we will have even less time to react.

In fact, this is not a new requirement. It exist on different flavors of
automotive Linux for about 10 years. Linux in cars should be able to
handle voltage drops for example on ignition and so on. The only new thing is
the attempt to mainline it.

Regards,
Oleksij
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