linux-kernel - Re: [RFC PATCH 3/3] pstore/ram: avoid atomic accesses for ioremapped regions

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Date:	Tue, 9 Apr 2013 21:10:37 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [RFC PATCH 3/3] pstore/ram: avoid atomic accesses for ioremapped regions

On Tue, Apr 9, 2013 at 8:08 PM, Rob Herring <robherring2@...il.com> wrote:
> From: Rob Herring <rob.herring@...xeda.com>
>
> For persistent RAM outside of main memory, the memory may have limitations
> on supported accesses. For internal RAM on highbank platform exclusive
> accesses are not supported and will hang the system. So atomic_cmpxchg
> cannot be used. This commit uses spinlock protection for buffer size and
> start updates on ioremapped regions instead.

I used atomics in persistent_ram to support persistent ftrace, which
now exists as PSTORE_FTRACE.  At some point during development I had
trouble with recursive tracing causing an infinite loop, so you may
want to test that calling out to spinlock functions with PSTORE_FTRACE
turned on and enabled doesn't cause a problem.
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