linux-kernel - RE: [RFC][PATCH -next] pstore: replace spin_lock with spin_trylock

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Date:	Wed, 28 Sep 2011 15:30:04 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Don Zickus <dzickus@...hat.com>
CC:	Seiji Aguchi <seiji.aguchi@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Matthew Garrett <mjg@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH -next] pstore: replace spin_lock with
 spin_trylock_irqsave in panic path

> That should be up to the backend, no?  ERST has two modes, only one which
> has a state machine.  The other is NVRAM which can probably handle
> simultaneous writes.  And I believe the EFI back-end can handle that as
> well.  That is why I was suggesting that the back-end return a failure.

ERST tries to provide a lot of flexibility to the platform on how to
make persistent space available.  If the platform has directly addressable
NVRAM - then ERST can point to it, so the "save" operation degenerates into
a simple write to the next available block.  But this isn't required. The
ERST buffer may be in normal memory, and the actions in the state machine
may trigger an SMI to make the BIOS copy it away to some safe place, or
the actions could ping a doorbell on a management controller which could
initiate a DMA transfer to pick up the buffer from memory.

-Tony
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