Messages in this thread | | | Date | Tue, 12 May 2015 10:06:01 -0500 | From | Suravee Suthikulanit <> | Subject | Re: [V3 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency |
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On 5/11/2015 8:20 PM, Rafael J. Wysocki wrote: > On Monday, May 11, 2015 05:16:27 PM Catalin Marinas wrote: >> On Fri, May 08, 2015 at 10:53:59PM +0200, Rafael J. Wysocki wrote: >>> On Thursday, May 07, 2015 07:37:12 PM Suravee Suthikulpanit wrote: >>>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig >>>> index ab2cbb5..7822149 100644 >>>> --- a/drivers/acpi/Kconfig >>>> +++ b/drivers/acpi/Kconfig >>>> @@ -54,6 +54,12 @@ config ACPI_GENERIC_GSI >>>> config ACPI_SYSTEM_POWER_STATES_SUPPORT >>>> bool >>>> >>>> +config ACPI_CCA_REQUIRED >>>> + bool >>>> + >>>> +config ARM64_SUPPORT_ACPI_CCA_ZERO >>> >>> Hmm. I guess the Arnd's idea what to simply use CONFIG_ARM64 directly instead >>> of adding this new option. >> >> I agree. >> >>>> +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), >>>> + * we would rely on arch-specific cache maintenance for >>>> + * non-coherence DMA operations if architecture specifies >>>> + * _XXX_SUPPORT_CCA_ZERO. Otherwise, we do not support >>>> + * DMA on this device and fallback to arch-specific default >>>> + * handling. >>>> + * >>>> + * 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. >>>> + */ >>>> + return adev && (adev->flags.is_coherent || >>>> + (adev->flags.cca_seen && >>>> + IS_ENABLED(CONFIG_ARM64_SUPPORT_ACPI_CCA_ZERO))); >>> >>> So what exactly would be wrong with using IS_ENABLED(CONFIG_ARM64) here? >> >> I'm not sure I follow why we need to check for ARM64 here at all. Can we >> not just have something like: >> >> return adev && (!IS_ENABLED(CONFIG_ACPI_CCA_REQUIRED) || >> adev->flags.cca_seen) > > If _CCA returns 0 on non-ARM64, DMA is not supported for this device, so > in that case the function should return 'false' while the above check will > make it return 'true'. >
The main idea is basically to allow architecture to decide if it wants to specify if it wants to support _CCA=0. Currently, there are two approaches. 1. Do not support and disable DMA 2. Support and default to what architecture would normally do for non-coherent DMA.
Since, ARM64 being the only platform, which supports ACPI and would support _CCA=0. I can just put CONFIG_ARM64 then as Arnd and Rafael mentioned.
Thanks, Suravee
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