linux-kernel - Re: [V3 PATCH 1/5] ACPI / scan: Parse

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Message-ID: <20150511161626.GI18655@e104818-lin.cambridge.arm.com>
Date:	Mon, 11 May 2015 17:16:27 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	thomas.lendacky@....com, linux-crypto@...r.kernel.org,
	herbert@...dor.apana.org.au, arnd@...db.de,
	linaro-acpi@...ts.linaro.org, will.deacon@....com,
	linux-kernel@...r.kernel.org, al.stone@...aro.org,
	linux-acpi@...r.kernel.org, netdev@...r.kernel.org,
	leo.duran@....com, hanjun.guo@...aro.org, msalter@...hat.com,
	grant.likely@...aro.org, davem@...emloft.net,
	linux-arm-kernel@...ts.infradead.org, lenb@...nel.org
Subject: Re: [V3 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

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)

-- 
Catalin
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