linux-kernel - Re: [PATCH 0/2] This patch introduces a feature to force gpio-poweroff module

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Date:   Mon, 30 Sep 2019 18:32:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksandr Suvorov <oleksandr.suvorov@...adex.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        Jamie Lentin <jm@...tin.co.uk>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Igor Opaniuk <igor.opaniuk@...adex.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 0/2] This patch introduces a feature to force
 gpio-poweroff module

On Mon, Sep 30, 2019 at 02:11:59PM +0000, Oleksandr Suvorov wrote:
> Hi Andrew,
> 
> On Mon, Sep 30, 2019 at 3:16 PM Andrew Lunn <andrew@...n.ch> wrote:
> >
> > On Mon, Sep 30, 2019 at 10:35:36AM +0000, Oleksandr Suvorov wrote:
> > > to register its own pm_power_off handler even if someone has registered
> > > this handler earlier.
> > > Useful to change a way to power off the system using DT files.
> >
> > Hi Oleksandr
> >
> > I'm not sure this is a good idea. What happens when there are two
> > drivers using forced mode? You then get which ever is register last.
> > Non deterministic behaviour.
> 
> You're right, we have to handle a case when gpio-poweroff fails to
> power the system off. Please look at the
> 2nd version of the patchset.
> 
> There are 3 only drivers that forcibly register its own pm_power_off
> handler even if it has been registered before.
> 
> drivers/firmware/efi/reboot.c - supports chained call of next
> pm_power_off handler if its own handler fails.
> 
> arch/x86/platform/iris/iris.c, drivers/char/ipmi/ipmi_poweroff.c -
> don't support calling of next pm_power_off handler.
> Looks like these drivers should be fixed too.
> 
> All other drivers don't change already initialized pm_power_off handler.
> 
> > What is the other driver which is causing you problems? How is it
> > getting probed? DT?
> 
> There are several PMUs, RTCs, watchdogs that register their own pm_power_off.
> Most of them, probably not all, are probed from DT.

And which specific one is causing you problems.

I don't like this forced parameter. No other driver is using it.

Maybe we should change this driver to support chained pm_power_off
handlers?

   Andrew