Re: [PATCH] pci: acpi: Generic function for setting up PCI device DMA coherency

[Suthikulpanit, Suravee]

Hi Bjorn,

On 8/25/2015 3:14 AM, Bjorn Helgaas wrote:
> On Mon, Aug 24, 2015 at 12:09 PM, Suravee Suthikulpanit
> <Suravee.Suthikulpanit@xxxxxxx> wrote:
>
> > > > commit 84cfb2213cd400fef227ec0d7829ec4e12895da9
> > > > Author: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > > 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 <bhelgaas@xxxxxxxxxx>
> >
> >
> > 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@xxxxxxxxxxxxxxx/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.

Ok. Let me simplify this and send out V2.

Thanks,
Suravee

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