linux-kernel - Re: [PATCH 1/8] x86: add alloc_coherent dma

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Message-Id: <20080821225038E.fujita.tomonori@lab.ntt.co.jp>
Date:	Thu, 21 Aug 2008 23:16:49 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	joerg.roedel@....com
Cc:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	muli@...ibm.com
Subject: Re: [PATCH 1/8] x86: add alloc_coherent dma_ops callback to GART
 driver

On Tue, 19 Aug 2008 16:32:39 +0200
Joerg Roedel <joerg.roedel@....com> wrote:

> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kernel/pci-gart_64.c |   21 +++++++++++++++++++++
>  1 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/pci-gart_64.c b/arch/x86/kernel/pci-gart_64.c
> index 4d8efb0..44a75a6 100644
> --- a/arch/x86/kernel/pci-gart_64.c
> +++ b/arch/x86/kernel/pci-gart_64.c
> @@ -506,6 +506,26 @@ error:
>  	return 0;
>  }
>  
> +/* allocate and map a coherent mapping */
> +static void *
> +gart_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_addr,
> +		    gfp_t flag)
> +{
> +	void *vaddr;
> +
> +	vaddr = (void *)__get_free_pages(flag, get_order(size));
> +	if (!vaddr)
> +		return NULL;
> +
> +	*dma_addr = gart_map_single(dev, __pa(vaddr), size, DMA_BIDIRECTIONAL);
> +	if (*dma_addr != bad_dma_address)
> +		return vaddr;

I'm not sure a rule is documented or not, but I think that IOMMUs
return zeroed memory wrt dma_alloc_coherent. The current pci-dma.c
does, so I think that it would be better to keep the current behavior.
--
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