Re: [PATCH V2 0/4] PCI: ACPI: Setting up DMA coherency for PCI device from _CCA attribute

From: Arnd Bergmann
Date: Tue Aug 25 2015 - 14:49:03 EST

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.

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