Messages in this thread | | | Date | Wed, 20 May 2015 06:52:03 -0500 | From | Suravee Suthikulanit <> | Subject | Re: [V4 PATCH 1/6] ACPI / scan: Parse _CCA and setup device coherency |
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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
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