On 5/20/2015 5:01 AM, Catalin Marinas wrote:
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.
Ok. That seems to be what Arnd would prefer as well. Let's just leave the support for _CCA=0 out until it is needed then.
Thanks, Suravee -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
