linux-kernel - Re: Problem with atomic accesses in pstore on some ARM CPUs

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Message-ID: <20160816132103.GD27088@arm.com>
Date:	Tue, 16 Aug 2016 14:21:03 +0100
From:	Will Deacon <will.deacon@....com>
To:	Guenter Roeck <groeck@...gle.com>
Cc:	Robin Murphy <robin.murphy@....com>,
	Kees Cook <keescook@...omium.org>,
	Jeffy Chen <jeffy.chen@...k-chips.com>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Douglas Anderson <dianders@...omium.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Problem with atomic accesses in pstore on some ARM CPUs

On Tue, Aug 16, 2016 at 06:14:53AM -0700, Guenter Roeck wrote:
> On Tue, Aug 16, 2016 at 3:32 AM, Robin Murphy <robin.murphy@....com> wrote:
> > On 16/08/16 00:19, Guenter Roeck wrote:
> >> we are having a problem with atomic accesses in pstore on some ARM
> >> CPUs (specifically rk3288 and rk3399). With those chips, atomic
> >> accesses fail with both pgprot_noncached and pgprot_writecombine
> >> memory. Atomic accesses do work when selecting PAGE_KERNEL protection.
> >
> > What's the pstore backed by? I'm guessing it's not normal DRAM.
> >
> 
> it is normal DRAM.

In which case, why does it need to be mapped with weird attributes?
Is there an alias in the linear map you can use?

Will