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

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Date:	Wed, 26 Aug 2015 09:36:28 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>
CC:	<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

Hi Arnd,

On 8/26/15 01:48, Arnd Bergmann wrote:
> 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

Thanks for pointing out. The CONFIG_ACPI_CCA_REQUIRED is already existed 
and selected in arch/arm64/Kconfig, and used for both PCI and non-PCI 
devices. I am not adding anything specific for the PCI case.

Although, I think WARN_ON(!CCA) when it is required is a good idea. I'll 
find a proper place for it.

Thanks,
Suravee.

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