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

[Suravee Suthikulpanit]

[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.

> > +	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.


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

Thanks,

Suravee
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