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