linux-kernel - Re: [RFC PATCH] arm: dma: Drop GFP

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Message-ID: <20111031103610.GG19187@n2100.arm.linux.org.uk>
Date:	Mon, 31 Oct 2011 10:36:10 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Marc Singer <elf@...ci.com>, LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	Sumit Bhattacharya <sumitb@...dia.com>
Subject: Re: [RFC PATCH] arm: dma: Drop GFP_COMP for DMA memory allocations

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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