Re: [V3 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Monday, May 11, 2015 05:16:27 PM Catalin Marinas wrote:
> On Fri, May 08, 2015 at 10:53:59PM +0200, Rafael J. Wysocki wrote:
> > On Thursday, May 07, 2015 07:37:12 PM Suravee Suthikulpanit wrote:
> > > diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> > > index ab2cbb5..7822149 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_CCA_REQUIRED
> > > +	bool
> > > +
> > > +config ARM64_SUPPORT_ACPI_CCA_ZERO
> > 
> > Hmm.  I guess the Arnd's idea what to simply use CONFIG_ARM64 directly instead
> > of adding this new option.
> 
> I agree.
> 
> > > +static inline bool acpi_dma_is_supported(struct acpi_device *adev)
> > > +{
> > > +	/**
> > > +	 * Currently, we mainly support _CCA=1 (i.e. is_coherent=1)
> > > +	 * This should be equivalent to specifyig dma-coherent for
> > > +	 * a device in OF.
> > > +	 *
> > > +	 * 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 specifies
> > > +	 * _XXX_SUPPORT_CCA_ZERO. Otherwise, we do not support
> > > +	 * DMA on this device and fallback to arch-specific default
> > > +	 * handling.
> > > +	 *
> > > +	 * For the case when _CCA is missing (i.e. cca_seen=0) but
> > > +	 * platform specifies ACPI_CCA_REQUIRED, we do not support DMA,
> > > +	 * and fallback to arch-specific default handling.
> > > +	 */
> > > +	return adev && (adev->flags.is_coherent ||
> > > +			(adev->flags.cca_seen &&
> > > +			 IS_ENABLED(CONFIG_ARM64_SUPPORT_ACPI_CCA_ZERO)));
> > 
> > So what exactly would be wrong with using IS_ENABLED(CONFIG_ARM64) here?
> 
> I'm not sure I follow why we need to check for ARM64 here at all. Can we
> not just have something like:
> 
> 	return adev && (!IS_ENABLED(CONFIG_ACPI_CCA_REQUIRED) ||
> 			adev->flags.cca_seen)

If _CCA returns 0 on non-ARM64, DMA is not supported for this device, so
in that case the function should return 'false' while the above check will
make it return 'true'.


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