linux-kernel - RE: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it is KCS

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Date:	Thu, 27 Aug 2015 01:35:36 +0000
From:	河合英宏 / KAWAI，HIDEHIRO 
	<hidehiro.kawai.ez@...achi.com>
To:	"'minyard@....org'" <minyard@....org>
CC:	"openipmi-developer@...ts.sourceforge.net" 
	<openipmi-developer@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 7/7] ipmi/kcs: Don't run the KCS state machine when it
 is KCS_IDLE

> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
> 
> On 08/24/2015 10:53 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
> >> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
> >>
> >> On 08/23/2015 08:52 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
> >>>> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
> >>>>
> >>>> On 08/17/2015 09:54 PM, 河合英宏 / KAWAI，HIDEHIRO wrote:
> >>>>>> From: Corey Minyard [mailto:tcminyard@...il.com] On Behalf Of Corey Minyard
> >>>>>>
> >>>>>> This patch will break ATN handling on the interfaces.  So we can't do this.
> >>>>> I understand.  So how about doing like this:
> >>>>>
> >>>>> 	/* All states wait for ibf, so just do it here. */
> >>>>> -	if (!check_ibf(kcs, status, time))
> >>>>> +	if (kcs->state != KCS_IDLE && !check_ibf(kcs, status, time))
> >>>>> 		return SI_SM_CALL_WITH_DELAY;
> >>>>>
> >>>>> I think it is not necessary to wait IBF when the state is IDLE.
> >>>>> In this way, we can also handle the ATN case.
> >>>> I think it would be more reliable to go up a level and add a timeout.
> >>> It may be so, but we should address this issue separately (at least
> >>> I think above solution reasonably solves the issue).
> >>>
> >>> This issue happens after all queued messages are processed or dropped
> >>> by timeout.  There is no current message.  So what should we set
> >>> a timeout against?  We can add a timeout into my new flush_messages(),
> >>> but that is meaningful only in panic context.  That doesn't help
> >>> in normal context; we would perform a busy loop of smi_event_handler()
> >>> and schedule() in ipmi_thread().
> >> I'm a little confused here.  Is the problem that the ATN bit is stuck
> >> high?  If so, it's going to be really hard to work around this without
> >> breaking ATN handling.
> > Sorry for my insufficient explanation.  I assume the case where
> > IBF bit is always 1.  I don't know what happens when
> > BMC hangs up, but I guess IBF stays in 1 because my server's
> > BMC behaves as such while rebooting.
> >
> Ok, your patch above makes sense, then.  IBF is irrelevant when in idle
> state,
> so ignore it then, and then in your case it will return KCS_IDLE and
> cause that
> operation to complete.  I'm ok with the patch you posted above, I think
> it will
> work correctly and solve the problem.
> 
> I would like a detailed comment, though, so people (forgetful people
> like me :)
> can figure out why it is there.

Sure.  I'll post the revised version with detailed comment and
description later including PATCH 6/7.

Thanks,

Hidehiro Kawai