20 May
2015
20 May
'15
11:52 a.m.
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