From mboxrd@z Thu Jan  1 00:00:00 1970
From: sergei.shtylyov@cogentembedded.com (Sergei Shtylyov)
Date: Thu, 20 Jun 2013 17:04:32 +0400
Subject: [PATCH] ARM: dma: Drop __GFP_COMP for iommu dma memory allocations
In-Reply-To: <1371731460-15316-1-git-send-email-rizhao@nvidia.com>
References: <1371731460-15316-1-git-send-email-rizhao@nvidia.com>
Message-ID: <51C2FDE0.4060206@cogentembedded.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hello.

On 20-06-2013 16:31, Richard Zhao wrote:

> __iommu_alloc_buffer wants to split pages after allocation in order to
> reduce the memory footprint. This does not work well with __GFP_COMP
> pages, so drop this flag before allocation

> One failure example is snd_malloc_dev_pages call dma_alloc_coherent with
> __GFP_COMP.

> Signed-off-by: Richard Zhao <rizhao@nvidia.com>
> ---
>   arch/arm/mm/dma-mapping.c |    9 +++++++++
>   1 file changed, 9 insertions(+)

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index ef3e0f3..f7efffd 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1314,6 +1314,15 @@ static void *arm_iommu_alloc_attrs(struct device *dev, size_t size,
>   	if (gfp & GFP_ATOMIC)
>   		return __iommu_alloc_atomic(dev, size, handle);
>
> +	/*
> +	 * Following is a work-around (a.k.a. hack) to prevent pages
> +	 * with __GFP_COMP being passed to split_page() which cannot
> +	 * handle them.  The real problem is that this flag probably
> +	 * should be 0 on ARM as it is not supported on this
> +	 * platform; see CONFIG_HUGETLBFS.
> +	 */
> +	gfp &= ~(__GFP_COMP);

    Hm, what exactly is the sense you meant in using ()?

WBR, Sergei