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:

quoted

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.

quoted

+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)

-- 
Catalin