linux-kernel - Re: [PATCH v2 1/5] printk/nmi: Generic solution for safe printk in NMI

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Message-ID: <20151130142545.GB8047@pathway.suse.cz>
Date:	Mon, 30 Nov 2015 15:25:45 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Max Filippov <jcmvbkbc@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Jiri Kosina <jkosina@...e.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"maintainer:X86 ARCHITECTURE..." <x86@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"moderated list:BLACKFIN ARCHITEC..." 
	<adi-buildroot-devel@...ts.sourceforge.net>,
	"open list:CRIS PORT" <linux-cris-kernel@...s.com>,
	Linux/MIPS Mailing List <linux-mips@...ux-mips.org>,
	linuxppc-dev@...ts.ozlabs.org,
	linux-s390 <linux-s390@...r.kernel.org>,
	"open list:SUPERH" <linux-sh@...r.kernel.org>,
	"open list:SPARC + UltraSPAR..." <sparclinux@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] printk/nmi: Generic solution for safe printk in
 NMI

On Fri 2015-11-27 17:26:16, Max Filippov wrote:
Hi Max,

> > Another exception is Xtensa architecture that uses just a
> > fake NMI.
> 
> It's called fake because it's actually maskable, but sometimes
> it is safe to use it as NMI (when there are no other IRQs at the
> same priority level and that level equals EXCM level). That
> condition is checked in arch/xtensa/include/asm/processor.h
> So 'fake' here is to avoid confusion with real NMI that exists
> on xtensa (and is not currently used in linux), otherwise code
> that runs in fake NMI must follow the NMI rules.
> 
> To make xtensa compatible with your change we can add a
> choice whether fake NMI should be used to kconfig. It can
> then set HAVE_NMI accordingly. I'll post a patch for xtensa.

Thanks a lot for explanation. I'll wait for the destiny of
the patch adding CONFIG_XTENSA_FAKE_NMI. It is not easy
for me to review. Anyway, we could select HAVE_NMI for
Xtensa anytime later if this patchset goes in earlier.

Best Regards,
Petr
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