linux-kernel - Re: [PATCHv6 3/5] common: dma-mapping: Introduce common remapping functions

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Date:	Fri, 8 Aug 2014 15:45:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Laura Abbott <lauraa@...eaurora.org>
Cc:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Russell King <linux@....linux.org.uk>,
	David Riley <davidriley@...omium.org>,
	linux-arm-kernel@...ts.infradead.org,
	Ritesh Harjain <ritesh.harjani@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Thierry Reding <thierry.reding@...il.com>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCHv6 3/5] common: dma-mapping: Introduce common remapping
 functions

On Fri,  8 Aug 2014 13:23:15 -0700 Laura Abbott <lauraa@...eaurora.org> wrote:

> 
> For architectures without coherent DMA, memory for DMA may
> need to be remapped with coherent attributes. Factor out
> the the remapping code from arm and put it in a
> common location to reduce code duplication.
> 
> As part of this, the arm APIs are now migrated away from
> ioremap_page_range to the common APIs which use map_vm_area for remapping.
> This should be an equivalent change and using map_vm_area is more
> correct as ioremap_page_range is intended to bring in io addresses
> into the cpu space and not regular kernel managed memory.
> 
> ...
>
> @@ -267,3 +269,68 @@ int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
>  	return ret;
>  }
>  EXPORT_SYMBOL(dma_common_mmap);
> +
> +/*
> + * remaps an allocated contiguous region into another vm_area.
> + * Cannot be used in non-sleeping contexts
> + */
> +
> +void *dma_common_contiguous_remap(struct page *page, size_t size,
> +			unsigned long vm_flags,
> +			pgprot_t prot, const void *caller)
> +{
> +	int i;
> +	struct page **pages;
> +	void *ptr;
> +
> +	pages = kmalloc(sizeof(struct page *) << get_order(size), GFP_KERNEL);
> +	if (!pages)
> +		return NULL;
> +
> +	for (i = 0; i < (size >> PAGE_SHIFT); i++)
> +		pages[i] = page + i;

Assumes a single mem_map[] array.  That's not the case for sparsemem
(at least).


> +	ptr = dma_common_pages_remap(pages, size, vm_flags, prot, caller);
> +
> +	kfree(pages);
> +
> +	return ptr;
> +}
> +

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