From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>,
        thomas.lendacky@amd.com, linux-crypto@vger.kernel.org,
        herbert@gondor.apana.org.au, arnd@arndb.de,
        linaro-acpi@lists.linaro.org, will.deacon@arm.com,
        linux-kernel@vger.kernel.org, al.stone@linaro.org,
        linux-acpi@vger.kernel.org, netdev@vger.kernel.org, leo.duran@amd.com,
        hanjun.guo@linaro.org, msalter@redhat.com, grant.likely@linaro.org,
        davem@davemloft.net, linux-arm-kernel@lists.infradead.org,
        lenb@kernel.org
Subject: Re: [V3 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency
Date: Tue, 12 May 2015 03:20:04 +0200
Message-ID: <1664523.WMm4AqWTY5@vostro.rjw.lan>
User-Agent: KMail/4.11.5 (Linux/4.0.0+; KDE/4.11.5; x86_64; ; )
In-Reply-To: <20150511161626.GI18655@e104818-lin.cambridge.arm.com>
References: <1431045436-8690-1-git-send-email-Suravee.Suthikulpanit@amd.com> <3684853.vaQGhc4jR5@vostro.rjw.lan> <20150511161626.GI18655@e104818-lin.cambridge.arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="utf-8"
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2488
Lines: 64

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/