On 04/29/2015 09:03 AM, Arnd Bergmann wrote:
On Wednesday 29 April 2015 08:44:09 Suravee Suthikulpanit wrote:+ device->flags.cca_seen = 1; + } else if (IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) { + /* + * Architecture has specified that if the device + * can do DMA, it must have ACPI _CCA object. + * Here, there could be two cases: + * 1. Not DMA-able device. + * 2. DMA-able device, but missing _CCA object. + * + * In both cases, we will default to dma non-coherent. + */ + cca = 0; + } else { + /* + * If architecture does not specify that device must + * specify ACPI _CCA (e.g. x86), we default to use + * dma coherent. + */ + cca = 1; + }What does it mean here if a device does DMA but is not coherent? Do you have an example of a server that needs this? Can we please make the default for ARM64 cca=1 as well? Arnd
Actually, I am trying to implement the logic for when missing _CCA to be consistent with the behavior when the devicetree entry does not specify "dma-coherent" property. IIUC, in such case, Linux will default to using non-coherent DMA.
Thanks, Suravee -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
