Re: [RFC PATCH] arm: dma: Drop GFP_COMP for DMA memory allocations

From: Russell King - ARM Linux
Date: Mon Oct 31 2011 - 06:39:35 EST


On Fri, Oct 28, 2011 at 03:18:52PM -0600, Stephen Warren wrote:
> I believe the patch below was once posted to solve this for ARM, but never
> got picked up. Evidently, AVR32 did pick it up. I'm wondering if we should
> pick this up for ARM now, or if there's some other solution?

Well, Nick did talk about a solution using GFP_USERMAP in one of those
threads, which doesn't seem to have gone anywhere. So I guess we need
this patch.

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 82a093c..93b86e6 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -308,6 +308,13 @@ __dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp,
> struct page *page;
> void *addr;
>
> + /* 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_HUGETLB_PAGE. */

I don't think this comment makes sense anymore - HUGETLB_PAGE doesn't
have any help text.

> + gfp &= ~(__GFP_COMP);
> +
> *handle = ~0;
> size = PAGE_ALIGN(size);
>
> --
> 1.7.0.4
>
>
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