Date:	Wed, 29 Oct 2014 13:55:49 +0100
From:	Romain Perier <romain.perier@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com,
	devicetree <devicetree@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>, j-keerthy@...com,
	nsekhar@...com, Felipe Balbi <balbi@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	t-kristo@...com, Lokesh Vutla <lokeshvutla@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Benoît Cousson <bcousson@...libre.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v2 00/20] rtc: omap: fixes and power-off feature

Johan:. do you really plan to use this "poweroff-source" property ? As
you proposed a renaming few days ago...
I don't really want to waste time to propose patches to fix things
incrementally and rename it if the old one is used...

Romain

2014-10-29 13:34 GMT+01:00 Johan Hovold <johan@...nel.org>:
> On Tue, Oct 28, 2014 at 03:16:10PM +0000, Russell King - ARM Linux wrote:
>> On Tue, Oct 28, 2014 at 02:12:57PM +0100, Johan Hovold wrote:
>> > That's not what I was trying to refer to. But the patch set explicitly
>> > allows for multiple, prioritised power-off handlers, which can power
>> > off a board in different ways and with various degrees of success.
>> > Specifically, it allows for fallback handlers in case one or more
>> > power-off handlers fail.
>> >
>> > So if we allow for that, what is to prevent the final power-off handler
>> > from failing? And should this not be logged by arch code in the same way
>> > as failure to restart is?
>>
>> And how is that different from having a set of power-off handlers, and
>> reporting when each individual one fails?  Don't you want to know if
>> your primary high priority reboot handler fails, just as much as you
>> want to know if your final last-resort power-off handler fails?
>
> Good point. Failed power-off should probably be logged by the power-off
> call chain implementation (which seems to makes notifier chains a bad
> fit).
>
> And what about any power-off latencies? Should this always be dealt with
> in the power-off handler?
>
> Again, if it's predictable and high, as in the OMAP RTC case, it should
> go in the handler. But what if it's just normal bus latencies
> (peripheral busses, i2c, or whatever people may come up with)?
>
> Should there always be a short delay before calling the next handler?
>
>> Or different from having no power-off handlers.
>
> That is actually quite different, as in that case we call machine_halt
> instead (via kernel_halt).
>
>> Here's the x86 code:
>>
>> void machine_power_off(void)
>> {
>>         machine_ops.power_off();
>> }
>>
>> struct machine_ops machine_ops = {
>>         .power_off = native_machine_power_off,
>> ...
>>
>> static void native_machine_power_off(void)
>> {
>>         if (pm_power_off) {
>>                 if (!reboot_force)
>>                         machine_shutdown();
>>                 pm_power_off();
>>         }
>>         /* A fallback in case there is no PM info available */
>>         tboot_shutdown(TB_SHUTDOWN_HALT);
>> }
>>
>> void tboot_shutdown(u32 shutdown_type)
>> {
>>         void (*shutdown)(void);
>>
>>         if (!tboot_enabled())
>>                 return;
>>
>> See - x86 can very well just fall straight back out of machine_power_off()
>> if there's no pm_power_off() hook and tboot is not enabled.
>
> I never doubted that, but is the right thing to do? Not all arches do it
> that way.
>
> And what about the killing of init? Shall we simply consider that a
> systemd bug?
>
>         case LINUX_REBOOT_CMD_POWER_OFF:
>                 kernel_power_off();
>                 do_exit(0);
>                 break;
>
> If power-off fails (for whatever reason), do_exit(0) will trigger a
> panic when called from PID 1.
>
> Johan
>
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