linux-kernel - Re: [PATCH v8 02/21] acpi: fix acpi_os

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Message-ID: <20150204175256.GH26006@e104818-lin.cambridge.arm.com>
Date:	Wed, 4 Feb 2015 17:52:56 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	"msalter@...hat.com" <msalter@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
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	Mark Rutland <Mark.Rutland@....com>,
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	<linux-arm-kernel@...ts.infradead.org>,
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	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64

On Wed, Feb 04, 2015 at 04:16:34PM +0000, Timur Tabi wrote:
> On 02/04/2015 10:08 AM, Mark Salter wrote:
> > acpi_os_remap() is used to map ACPI tables. These tables may be in ram
> > which are already included in the kernel's linear RAM mapping. So we
> > need ioremap_cache to avoid two mappings to the same physical page
> > having different caching attributes.
> 
> Would it be possible to modify ioremap() so that it can tell whether the 
> memory is already mapped in some way, and then use a compatible remapping?

No. We have some semantics for ioremap() and it should return
non-cacheable mapping.

ioremap_cache() checks whether the page is RAM already and returns the
existing kernel linear mapping on arm64.

-- 
Catalin
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