On Friday 16 January 2015 16:40:28 Arnd Bergmann wrote: > On Friday 16 January 2015 15:33:20 Will Deacon wrote: > > On Fri, Jan 16, 2015 at 03:14:13PM +0000, Arnd Bergmann wrote: > > > On Friday 16 January 2015 14:55:45 Will Deacon wrote: > > > > On Fri, Jan 16, 2015 at 02:45:30PM +0000, Tom Lendacky wrote: > > > > > I have tested ACPI-enablement patches for the amd-xgbe/amd-xgbe-phy > > > > > drivers that I'm about to submit upstream with the V7 patch series > > > > > on the AMD Seattle server platform. There does not appear to be support > > > > > for the _CCA attribute in this patch series. The amd-xgbe driver will > > > > > setup the device domain and cache attributes based on the presence of > > > > > this attribute, but it requires the arch support to assign the proper > > > > > DMA operations in order for it to all work correctly. > > > > > > > > > > Overriding the _CCA attribute in the driver, I was able to successfully > > > > > test the driver and this patch series. > > > > > > > > Hopefully this will all be addressed when the IORT parts of ACPI have > > > > settled down (the current proposal allows for these attributes to be > > > > described as well as their interaction with things like IOMMUs). > > > > > > > > In the meantime, are you falling back to non-coherent DMA? If so, what > > > > attributes have you settled on? We need to be really careful not to > > > > corrupt data during cache invalidatation when mapping a non-coherent > > > > buffer for the CPU. > > > > > > I think in case of ACPI we should use cache-coherent as the default, > > > as this is what all servers will use for DMA masters. > > > > I don't agree. The dma-coherent we have for device-tree isn't nearly > > expressive enough for the kind of things we want to describe and there's > > no reason to make the same mistake in ACPI, especially as it *is* being > > addressed by IORT. If we run with _CCA, then we're going to be stuck > > supporting something that isn't fit for purpose and which will likely be > > abused to describe both fixed features of the system and software > > configuration preferences. It also opens up a can of worms if we have to > > support a mixture of _CCA and IORT in the future. > > > > Or are you suggesting that we ignore _CCA and just assume cache-coherency? > > In that case, how do we support systems that aren't cache coherent, where > > not being cache coherent includes devices that require either device or > > IOMMU configuration to enable cacheable transactions? > > I was thinking we'd ignore _CCA because as you say a simple on/off flag > would not be enough to describe what we have to do for noncoherent > devices. I can't think of any reason why a server hardware would include > noncoherent devices, so if they are configurable they should be configured > into coherent mode by the firmware. To clarify: I don't think we should just ignore _CCA in Linux, but instead see if it lists the device as coherent and warn loudly if it's configured as noncoherent, then set the dma-mask pointer to NULL to prevent DMA from being started on it. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
