linux-kernel - Re: [PATCH V2 0/4] PCI: ACPI: Setting up DMA coherency for PCI device from

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Message-ID: <240091906.Gl2z931jjW@wuerfel>
Date:	Tue, 25 Aug 2015 20:48:24 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	bhelgaas@...gle.com, rjw@...ysocki.net, lenb@...nel.org,
	catalin.marinas@....com, will.deacon@....com,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, hanjun.guo@...aro.org
Subject: Re: [PATCH V2 0/4] PCI: ACPI: Setting up DMA coherency for PCI device from _CCA attribute

On Wednesday 26 August 2015 00:33:25 Suravee Suthikulpanit wrote:
> This patch adds support to setup DMA coherency for PCI device using
> the ACPI _CCA attribute. According to the ACPI spec, the _CCA attribute
> is required for ARM64. Therefore, this patch is a pre-req for ACPI PCI
> support for ARM64 which is currently in development.
> 
> Also, this should not affect other architectures that does not define 
> CONFIG_ACPI_CCA_REQUIRED, since the default value is coherent.
> 

We only support ACPI on SBSA compliant platforms, and SBSA mandates
cache-coherent PCI, so I don't think this is actually needed,
just use coherent all the time and do WARN_ON(!CCA) to catch people
that try to incorrectly use ACPI on a non-SBSA platform.

	Arnd
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