On Fri, May 15, 2015 at 04:23:09PM -0500, Suravee Suthikulpanit wrote:
> +static inline bool acpi_dma_is_supported(struct acpi_device *adev)
> +{
> + /**
> + * Currently, we mainly support _CCA=1 (i.e. is_coherent=1)
> + * This should be equivalent to specifyig dma-coherent for
> + * a device in OF.
> + *
> + * For the case when _CCA=0 (i.e. is_coherent=0 && cca_seen=1),
> + * There are two approaches:
> + * 1. Do not support and disable DMA.
> + * 2. Support but rely on arch-specific cache maintenance for
> + * non-coherence DMA operations. ARM64 is one example.
> + *
> + * For the case when _CCA is missing (i.e. cca_seen=0) but
> + * platform specifies ACPI_CCA_REQUIRED, we do not support DMA,
> + * and fallback to arch-specific default handling.
> + *
> + * See acpi_init_coherency() for more info.
> + */
> + return adev && (adev->flags.is_coherent ||
> + (adev->flags.cca_seen && IS_ENABLED(CONFIG_ARM64)));
> +}
I don't particularly like the check for CONFIG_ARM64 here but I
understand why it was added (I had the wrong impression that x86 can
cope with _CCA = 0).
Alternatively, we could leave it out (together with cca_seen) until
someone comes forward with a real use-case for _CCA = 0 on arm64. One
platform I'm aware of is Juno but even though it boot with ACPI, I
wouldn't call it a server platform.
--
Catalin
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