Re: [PATCH V3 2/4] ACPI/scan: Clean up acpi_check_dma

[Suravee Suthikulpanit]

Hi Bjorn/Rafael,

Let me redo the patch with enum then. At least, that's more clear to 
everyone.

Thanks,

Suravee

On 10/19/15 21:17, Bjorn Helgaas wrote:
> On Tue, Oct 13, 2015 at 06:53:28PM -0500, Suravee Suthikulanit wrote:
> > Bjorn / Rafael,
> >
> > On 10/13/2015 10:52 AM, Suravee Suthikulpanit wrote:
> > > On 09/14/2015 09:34 AM, Bjorn Helgaas wrote:
> > > > [..]
> > > > I think acpi_check_dma_coherency() is better, but only slightly.  It
> > > > still doesn't give a hint about the *sense* of the return value.  I
> > > > think it'd be easier to read if there were two functions, e.g.,
> > >
> > > I have been going back-and-forth between the current version, and the
> > > two-function-approach in the past. I can definitely go with this route
> > > if you would prefer. Although, if acpi_dma_is_coherent() == 0, it would
> > > be ambiguous whether DMA is not supported or non-coherent DMA is
> > > supported. Then, we would need to call acpi_dma_is_supported() to find
> > > out. So, that's okay with you?
> >
> > Thinking about this again, I still think having one API (which can
> > tell whether DMA is supported or not, and if so whether it is
> > coherent or non-coherent) would be the least confusing and least
> > error prone.
> >
> > What if we would just have:
> >
> >      enum dev_dma_type acpi_get_dev_dma_type(struct acpi_device *adev);
> >
> > where:
> >      enum dev_dma_type {
> >          DEV_DMA_NOT_SUPPORTED,
> >          DEV_DMA_NON_COHERENT,
> >          DEV_DMA_COHERENT,
> >      };
> >
> > This would probably mean that we should modify
> > drivers/base/property.c to replace:
> >      bool device_dma_is_coherent()
> > to:
> >      enum dev_dma_type device_get_dma_type()
> >
> > We used to discuss the enum approach in the past
> > (https://lkml.org/lkml/2015/8/25/868). But we only considered at the
> > ACPI level at the time. Actually, this should also reflect in the
> > property.c.
> >
> > At this point, only drivers/crypto/ccp/ccp-platform.c and
> > drivers/net/ethernet/amd/xgbe/xgbe-main.c are calling the
> > device_dma_is_coherent(). So, it should be easy to change this API.
>
> OK, I'm fine with either the enum or Rafael's 0/1/-ENOTSUPP idea.
>
> Bjorn
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