Re: [RFC] /dev/ioasid uAPI proposal

Christoph Hellwig
2021-06-30T06:54:54Z

On Tue, Jun 08, 2021 at 09:20:29AM +0800, Jason Wang wrote:
> "
>
> 6.2.17 _CCA (Cache Coherency Attribute) The _CCA object returns whether or
> not a bus-master device supports hardware managed cache coherency. Expected
> values are 0 to indicate it is not supported, and 1 to indicate that it is
> supported. All other values are reserved.
>
> ...
>
> On Intel platforms, if the _CCA object is not supplied, the OSPM will assume
> the devices are hardware cache coherent.
>
> "

_CCA is mostly used on arm/arm64 platforms to figure out if a device
needs non-coherent DMA handling in the DMA API or not. It is not
related to the NoSnoop TLPs that override the setting for an otherwise
coherent device.