Re: [V2 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

Rafael J. Wysocki
2015-05-06T21:56:44Z

On Tuesday, May 05, 2015 11:15:37 PM Suravee Suthikulpanit wrote:
> [RESEND]
>
> On 5/5/15 15:36, Rafael J. Wysocki wrote:
> > On Tuesday, May 05, 2015 10:12:05 AM Suravee Suthikulpanit wrote:
> >> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> >> index ab2cbb5..dd386e9 100644
> >> --- a/drivers/acpi/Kconfig
> >> +++ b/drivers/acpi/Kconfig
> >> @@ -54,6 +54,12 @@ config ACPI_GENERIC_GSI
> >> config ACPI_SYSTEM_POWER_STATES_SUPPORT
> >> bool
> >>
> >> +config ACPI_MUST_HAVE_CCA
> >
> > ACPI_CCA_REQUIRED maybe?
>
> Sure.
>
> >
> >> + bool
> >> +
> >> +config ACPI_SUPPORT_CCA_ZERO
> >
> > I guess this means "we support devices that can DMA, but are not coherent".
> > right?
>
> Yes, basically when _CCA=0.

So what about

ARCH_SUPPORT_CACHE_INCOHERENT_DMA

or something similar?

> >> + bool
> >> +
> >> config ACPI_SLEEP
> >> bool
> >> depends on SUSPEND || HIBERNATION
> >> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
> >> index 4bf7559..a6feca4 100644
> >> --- a/drivers/acpi/acpi_platform.c
> >> +++ b/drivers/acpi/acpi_platform.c
> >> @@ -108,9 +108,11 @@ 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 {
> >
> > Please add braces to both branches when making such changes (as per CodingStyle).
> >
>
> OK.
>
> >> + acpi_setup_device_dma(adev, &pdev->dev);
> >
> > Why do we need to do that here (for the second time)?
>
> Because we are calling:
> acpi_create_platform_device()
> |--> platform_device_register_device_full()
> |-->platform_device_alloc()
>
> This creates platform_device, which allocate a new platform_device->dev.
> This is not the same as the original acpi_device->dev that was created
> during acpi_add_single_object(). So, we have to set up the device
> coherency again.

Ah, so the second arg is different now.

Well, in that case, why do we need to set it up for the adev's dev member?

> >> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >> index 849b699..ac33b29 100644
> >> --- a/drivers/acpi/scan.c
> >> +++ b/drivers/acpi/scan.c
> >> @@ -11,6 +11,7 @@
> >> #include <linux/kthread.h>
> >> #include <linux/dmi.h>
> >> #include <linux/nls.h>
> >> +#include <linux/dma-mapping.h>
> >>
> >> #include <asm/pgtable.h>
> >>
> >> @@ -2137,6 +2138,66 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
> >> kfree(pnp->unique_id);
> >> }
> >>
> >> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev)
> >> +{
> >> + int coherent = acpi_dma_is_coherent(adev);
> >> +
> >> + /**
> >> + * Currently, we only support DMA for devices that _CCA=1
> >> + * since this seems to be the case on most ACPI platforms.
> >> + *
> >> + * For the case when _CCA=0 (i.e. is_coherent=0 && cca_seen=1),
> >> + * we would rely on arch-specific cache maintenance for
> >> + * non-coherence DMA operations if architecture enables
> >> + * CONFIG_ACPI_SUPPORT_CCA_ZERO.
> >> + *
> >> + * For the case when _CCA is missing but platform requires it
> >> + * (i.e. is_coherent=0 && cca_seen=0), we do not call
> >> + * arch_setup_dma_ops() and fallback to arch-specific default
> >> + * handling.
> >> + */
> >> + if (adev->flags.cca_seen) {
> >> + if (!coherent && !IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
> >> + return;
> >> + arch_setup_dma_ops(dev, 0, 0, NULL, coherent);
> >
> > Oh dear.
>
> I made a mistake here. This logic should also call arch_setup_dma_ops()
> when cca_seen=0 and coherent=1 (e.g. when _CCA is not required and
> default to coherent when it is missing). The current logic doesn't do that.
>
> >
> > What about
> >
> > if (adev->flags.cca_seen && (coherent || IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO)))
> > arch_setup_dma_ops(dev, 0, 0, NULL, coherent);
>
> What about:
> if (coherent ||
> (adev->flags.cca_seen &&
> IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
> arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

Yes, that works.

> > I wonder how this is going to affect x86/ia64 too?
> >
>
> This should not affect x86 since arch_setup_dma_ops() is currently not
> implement for x86, and default to NOP (see include/linux/dma-mapping.h).

OK

> Also, on x86, _CCA is not required and default to 1 if missing.

Well, that's the point. :-)

--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.