Message-ID: <554A6C6F.4030602@acm.org>
Date:	Wed, 06 May 2015 14:33:03 -0500
From:	Corey Minyard <minyard@....org>
To:	Mandeep Sandhu <mandeepsandhu.chd@...il.com>
CC:	openipmi-developer@...ts.sourceforge.net,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Openipmi-developer] Shutdown behavior with IPMI enabled

On 05/06/2015 12:23 PM, Mandeep Sandhu wrote:
>>> I have access to the BMC firmware and I saw that the way BMC handles
>>> "chassis power off" is by emulating a power button press for 6
>>> seconds. But since the host already shuts down in the meantime, the
>>> button press ends up power up the system again!
>> Well that's a very unusual interpretation of "power off".
> How do you think power off should've been handled by the BMC? Should
> it have requested the BIOS to put the CPU in the power off state (S5)?
> Mine is an Intel system and I guess the kernel too requests the BIOS
> for putting the CPU in S5 state (by writing to some BIOS register).

Certainly, it should just immediately power the system off.  There is a
soft shutdown option if you want a graceful shutdown.

The spec says:

    0 - power down. Force system into soft off (S4/S45) state. This is for
    ‘emergency’ management power down actions. The command
    does not initiate a clean shut-down of the operating system prior to
    powering down the system.

I would say the system in question is not compliant, to me, 6 seconds an
"force" are not the same thing :).

>> Well, theoretically, if the power off function completes, the system
>> should be powered off and therefore nothing else should run.  So there's
>> no real provision for not calling the other power off functions.
> I went through the code of ipmi_poweroff module and it seems that the
> driver ends up replacing the "pm_power_off" function with it's own
> ipmi_poweroff_function. So I assume only the IPMI power action should
> be performed. But it seems that there's some other path during the
> shutdown sequence which also switches off the system. If I disable
> ACPI (via kernel cmdline), then the kernel power off does not happen,
> and only IPMI is used.

Yes, the ACPI power off ties in through a different mechanism.

>>> If the host can shut itself down, it should not ask the BMC to do a
>>> power off or vice-versa.
>> I"m not sure I have a great solution.  You can, of course, not use the
>> ipmi_poweroff module.  I'm not sure of the utility of it in a modern
>> system.  In the past, before reliable ACPI and such, some systems didn't
>> have reliable power off function and IPMI was the only way to accomplish
>> this in some cases.  Which is why the function exists.
> Thanks for giving a background context to the poweroff module. I
> wasn't sure why or when is it needed.
>
>> Another option would be to spin in the ipmi power off function forever.
>> I'm not sure I like that option, either.
>>
>> It might be best to remove, or at least disable normally, the config
>> option in most systems.  That way systems that really needed it could
>> have it, but it wouldn't affect most people.
> Which config option do you refer to here? Something that disables the
> IPMI power off function?

Yes, CONFIG_IPMI_POWEROFF

-corey

> Thanks for your time.
>
> Regards,
> -mandeep
>
>> -corey
>>
>>> Thanks,
>>> -mandeep

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