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    SubjectRe: [PATCH v7 00/17] Introduce ACPI for ARM64 based on ACPI 5.1
    On Fri, Jan 16, 2015 at 03:14:13PM +0000, Arnd Bergmann wrote:
    > On Friday 16 January 2015 14:55:45 Will Deacon wrote:
    > > On Fri, Jan 16, 2015 at 02:45:30PM +0000, Tom Lendacky wrote:
    > > > 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


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