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From: Arnd Bergmann <arnd@arndb.de>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Mark Rutland <mark.rutland@arm.com>, arm@kernel.org,
        devicetree@vger.kernel.org, Kumar Gala <galak@codeaurora.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 2/2] arm64: dts: uniphier: change release address of spin-table
Date: Fri, 15 Apr 2016 20:48:05 +0200
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On Friday 15 April 2016 22:13:55 Masahiro Yamada wrote:
> 2016-04-15 22:05 GMT+09:00 Mark Rutland <mark.rutland@arm.com>:
> > On Fri, Apr 15, 2016 at 07:30:47PM +0900, Masahiro Yamada wrote:
> >> The 8-byte register located at 0x59801200 on this SoC is dedicated
> >> for waking up secondary CPUs.  We can use it and save normal memory.
> >
> > Generally, it is not safe to use MMIO registers to back spin-table. The
> > kernel maps the spin table location with cacheable attributes, so there
> > may be speculative accesses to any registes in the same (64K) page, and
> > a writeback may be larger than the 8-byte register width (which the
> > device might not accept, triggering an SError).
> >
> > Given that, I do not think this is a good idea.
> 
> I did not know this.  Thanks for your advice!
> 
> 
> Arnd, Olof
> 
> Please drop this patch.
> (I think 1/2 is still OK.)
> 

Should patch 1 be applied as a bugfix for 4.6 instead?

	Arnd