Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency

Arnd Bergmann
2015-04-29T14:03:35Z

On Wednesday 29 April 2015 08:44:09 Suravee Suthikulpanit wrote:
> + device->flags.cca_seen = 1;
> + } else if (IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) {
> + /*
> + * Architecture has specified that if the device
> + * can do DMA, it must have ACPI _CCA object.
> + * Here, there could be two cases:
> + * 1. Not DMA-able device.
> + * 2. DMA-able device, but missing _CCA object.
> + *
> + * In both cases, we will default to dma non-coherent.
> + */
> + cca = 0;
> + } else {
> + /*
> + * If architecture does not specify that device must
> + * specify ACPI _CCA (e.g. x86), we default to use
> + * dma coherent.
> + */
> + cca = 1;
> + }
>

What does it mean here if a device does DMA but is not coherent? Do you
have an example of a server that needs this?

Can we please make the default for ARM64 cca=1 as well?

Arnd