Re: [PATCH 2/2] ACPI / scan: Parse _CCA and setup device coherency

Arnd Bergmann
2015-04-29T16:25:26Z

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(). 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.

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?

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