Date: Wed, 4 Feb 2015 17:52:56 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: Timur Tabi <timur@codeaurora.org>
Cc: "msalter@redhat.com" <msalter@redhat.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "hanjun.guo@linaro.org" <hanjun.guo@linaro.org>,
        Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
        Mark Rutland <Mark.Rutland@arm.com>,
        "grant.likely@linaro.org" <grant.likely@linaro.org>,
        Will Deacon <Will.Deacon@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        "graeme.gregory@linaro.org" <graeme.gregory@linaro.org>,
        Sudeep Holla <Sudeep.Holla@arm.com>, "jcm@redhat.com" <jcm@redhat.com>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <Marc.Zyngier@arm.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Mark Brown <broonie@kernel.org>, Rob Herring <robh@kernel.org>,
        Robert Richter <rric@kernel.org>, Randy Dunlap <rdunlap@infradead.org>,
        Charles Garcia-Tobin <Charles.Garcia-Tobin@arm.com>,
        "phoenix.liyi@huawei.com" <phoenix.liyi@huawei.com>,
        Ashwin Chaugule <ashwinc@codeaurora.org>,
        "suravee.suthikulpanit@amd.com" <suravee.suthikulpanit@amd.com>,
        Mark Langsdorf <mlangsdo@redhat.com>,
        "wangyijing@huawei.com" <wangyijing@huawei.com>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linaro-acpi@lists.linaro.org" <linaro-acpi@lists.linaro.org>
Subject: Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64
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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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