On Mon, Aug 24, 2015 at 12:09 PM, Suravee Suthikulpanit
[off-list ref] wrote:

quoted

quoted

commit 84cfb2213cd400fef227ec0d7829ec4e12895da9
Author: Bjorn Helgaas [off-list ref]
Date:   Thu Aug 13 19:49:52 2015 -0500

     ACPI / scan: Rename acpi_check_dma() to acpi_dma_is_coherent()

     The name "acpi_check_dma()" doesn't give any much indication about
what
     exactly it checks.  The function also returns information both as a
normal
     return value and as the "bool *coherent" return parameter.  But
"*coherent"
     doesn't actually give any extra information: it is unchanged when
returning
     false and set to true when returning true.

     Rename acpi_check_dma() to acpi_dma_is_coherent() so the callers
read more
     naturally.  Drop the return parameter and just use the function
return
     value.

     Signed-off-by: Bjorn Helgaas [off-list ref]

This was because, at one point, we wanted to be able to differentiate
between the case _CCA=0 and missing _CCA in ARM64, where we would support
DMA (using arch-specific cache maintenance) if _CCA=0, and disable DMA when
missing _CCA on ARM64.

It seems like the logic is now required (please see
https://www.mail-archive.com/linux-usb at vger.kernel.org/msg62735.html). So,
we would need the true/false return, and the coherent variable to be able to
differentiate between the two cases.

Please let me know what you think.

It's hard for me to comment without seeing the actual patches.  I
think returning two values (_CCA-seen and coherent) is a confusing
interface.