Messages in this thread | | | Date | Wed, 29 Apr 2015 16:53:10 -0500 | From | Suravee Suthikulpanit <> | Subject | Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency |
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On 4/29/15 11:25, Arnd Bergmann wrote: > On Wednesday 29 April 2015 08:44:09 Suravee Suthikulpanit wrote: >> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c >> index 4bf7559..a4db208 100644 >> --- a/drivers/acpi/acpi_platform.c >> +++ b/drivers/acpi/acpi_platform.c >> @@ -108,9 +108,12 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev) >> if (IS_ERR(pdev)) >> dev_err(&adev->dev, "platform device creation failed: %ld\n", >> PTR_ERR(pdev)); >> - else >> + else { >> + arch_setup_dma_ops(&pdev->dev, 0, 0, NULL, >> + adev->flags.is_coherent); >> dev_dbg(&adev->dev, "created platform device %s\n", >> dev_name(&pdev->dev)); >> + } >> >> kfree(resources); >> > > Looking at this code in more detail, it seems that it unconditionally > sets pdevinfo.dma_mask = DMA_BIT_MASK(32), before calling > arch_setup_dma_ops().
I think that's just the default legacy value assigned when it first create the platform_device from acpi_device.
> This assignment should really done inside of arch_setup_dma_ops() > instead, which means we should implement that > function on all architectures that support ACPI.
> For the case where _CCA is missing (or coherency disabled, if you ask > me), we would not call that function.
Actually, I agree for the case of missing _CCA when needed, ACPI driver probably should not make assumption and leave the decision for the default underlying arch-specific default. Basically, it should not be calling arch_setup_dma_ops().
As for the case where _CCA=0, I think the ACPI driver should essentially communicate the information as HW is non-coherent as described in the spec, and should be calling arch_setup_dma_ops(dev, false). It is true that this in probably less-likely for the ARM64 server platforms. However, I would think that the ACPI driver should not be making such assumption.
> On a related note, I'm not sure how to handle different DMA masks here. > arch_setup_dma_ops() gets passed a size (and offset) argument, which should > match the DMA mask, but I don't know if there is a way to find out the > size from ACPI. Should we assume it's always 64-bit DMA capable?
Looking at the ACPI spec, it does have the _DMA object. IIUC, this can be used to describe DMA properties of a particular bus.
Method(_DMA, ResourceTemplate() { QWORDMemory( ResourceConsumer, PosDecode, // _DEC MinFixed, // _MIF MaxFixed, // _MAF Prefetchable, // _MEM ReadWrite, // _RW 0, // _GRA 0, // _MIN 0x1fffffff, // _MAX 0x200000000, // _TRA 0x20000000, // _LEN , , , ) }
I am not sure if this is an appropriate use for this object, but this seems to be similar to the dma-ranges property for OF, and probably can be used to specify baseaddr and size information when calling arch_setup_dma_ops().
> For legacy reasons, the default mask is probably best left at 32-bit, > but drivers are expected to call dma_set_mask() if they can do 64-bit DMA, > and that should fail based on the information provided by the platform > if the bus is not capable of doing that. > > Arnd >
However, on ARM64 the dma_base and size parameter for arch_setup_dma_ops() is currently not used, and only coherent flag is used. We probably should look at this separately. For the moment, we can probably say that if _CCA object is missing when needed, the ACPI driver won't set up dma_mask when creating platform_device, which should be equivalent to saying DMA is not supported.
Please let me know if this is acceptable, and I'll make change in V2 accordingly.
Thanks,
Suravee
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