linux-kernel - Re: [V2 PATCH 2/5] arm64 : Introduce support for ACPI

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Message-ID: <5549E834.1040305@arm.com>
Date:	Wed, 06 May 2015 11:08:52 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"lenb@...nel.org" <lenb@...nel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"al.stone@...aro.org" <al.stone@...aro.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"leo.duran@....com" <leo.duran@....com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"msalter@...hat.com" <msalter@...hat.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
Subject: Re: [V2 PATCH 2/5] arm64 : Introduce support for ACPI _CCA object

Hi Suravee,

On 05/05/15 16:12, Suravee Suthikulpanit wrote:
>  From http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf,
> section 6.2.17 _CCA states that ARM platforms require ACPI _CCA
> object to be specified for DMA-cabpable devices. This patch introduces
> ACPI_MUST_HAVE_CCA in arm64 Kconfig to specify such requirement.
>
> In this case of missing _CCA, arm64 would assign dummy_dma_ops
> to disable DMA capability of the device.
>
> Signed-off-by: Mark Salter <msalter@...hat.com>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> ---

[...]
> +static void __dummy_sync_single_for_cpu(struct device *dev,
> +					dma_addr_t dev_addr, size_t size,
> +					enum dma_data_direction dir)
> +{
> +}
> +
> +static void __dummy_sync_single_for_device(struct device *dev,
> +					   dma_addr_t dev_addr, size_t size,
> +					   enum dma_data_direction dir)
> +{
> +}

Minor point, but I don't see the need to have multiple dummy functions 
with identical signatures - just have a generic dummy_sync_single and 
assign it to both ops.

> +static void __dummy_sync_sg_for_cpu(struct device *dev,
> +				    struct scatterlist *sgl, int nelems,
> +				    enum dma_data_direction dir)
> +{
> +}
> +
> +static void __dummy_sync_sg_for_device(struct device *dev,
> +				       struct scatterlist *sgl, int nelems,
> +				       enum dma_data_direction dir)
> +{
> +}

Ditto here with dummy_sync_sg.

I wonder if there's any argument for putting the dummy DMA ops somewhere 
common, like drivers/base/dma-mapping.c?

Robin.

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