On Fri, Jan 16, 2015 at 03:14:13PM +0000, Arnd Bergmann wrote:

On Friday 16 January 2015 14:55:45 Will Deacon wrote:

quoted

On Fri, Jan 16, 2015 at 02:45:30PM +0000, Tom Lendacky wrote:

quoted

I have tested ACPI-enablement patches for the amd-xgbe/amd-xgbe-phy
drivers that I'm about to submit upstream with the V7 patch series
on the AMD Seattle server platform. There does not appear to be support
for the _CCA attribute in this patch series. The amd-xgbe driver will
setup the device domain and cache attributes based on the presence of
this attribute, but it requires the arch support to assign the proper
DMA operations in order for it to all work correctly.

Overriding the _CCA attribute in the driver, I was able to successfully
test the driver and this patch series.

Hopefully this will all be addressed when the IORT parts of ACPI have
settled down (the current proposal allows for these attributes to be
described as well as their interaction with things like IOMMUs).

In the meantime, are you falling back to non-coherent DMA? If so, what
attributes have you settled on? We need to be really careful not to
corrupt data during cache invalidatation when mapping a non-coherent
buffer for the CPU.

I think in case of ACPI we should use cache-coherent as the default,
as this is what all servers will use for DMA masters.

Last time I heard in some call, it was agreed that _CCA properties
should always be present and Linux should not make any assumption (there
is no safe assumption here). While better options may appear in ACPI,
_CCA is what we currently have.

-- 
Catalin