linux-kernel - Re: [PATCH v4 01/15] ARM: export arm_pm

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Date:   Wed, 09 Jan 2019 08:24:04 +0100
From:   Lubomir Rintel <lkundrak@...sk>
To:     Russell King - ARM Linux <linux@...linux.org.uk>
Cc:     Andy Shevchenko <andy@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        platform-driver-x86@...r.kernel.org,
        James Cameron <quozl@...top.org>,
        Mark Rutland <mark.rutland@....com>,
        Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Sebastian Reichel <sre@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/15] ARM: export arm_pm_restart()

On Tue, 2019-01-08 at 23:31 +0000, Russell King - ARM Linux wrote:
> On Tue, Jan 08, 2019 at 06:58:04PM +0100, Lubomir Rintel wrote:
> > The OLPC XO 1.75 laptop is rebooted with a command to the Embedded
> > Controller. The EC driver should be a module, since most people don't need
> > it to be compiled in.
> 
> Why do you need this - is there a reason why you can't hook onto the
> restart_handler_list using register_restart_handler()?  The registered
> handlers are passed the command.

Actually, yes. The restart handlers are invoked in atomic context, but
the EC communication needs to block. (The 1.75 EC is actually a SPI
master: a command it initiated by poking a GPIO and waiting until EC
tells us it's ready to read a command.)

Sorry for not mentioning that earlier, I forgot that it is the case.

> I would rather this is not exported to modules, it is generally unsafe
> to hook stuff by directly poking function pointers from module code.

Lubo