linux-kernel - Re: [PATCH 2/2] arm64: dts: uniphier: change release address of spin-table

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Message-ID: <CAK7LNARNUMkD79h-uG_EhRFr4gE2pDM8w57EddOMbt-mO0xc8A@mail.gmail.com>
Date:	Fri, 15 Apr 2016 22:13:55 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	arm@...nel.org, devicetree@...r.kernel.org,
	Kumar Gala <galak@...eaurora.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] arm64: dts: uniphier: change release address of spin-table

Hi Mark.

2016-04-15 22:05 GMT+09:00 Mark Rutland <mark.rutland@....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.)



-- 
Best Regards
Masahiro Yamada