Messages in this thread | | | Date | Wed, 29 Apr 2015 09:45:43 -0500 | From | Suravee Suthikulpanit <> | Subject | Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency |
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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
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