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

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Date:	Fri, 08 Aug 2014 16:25:58 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Riley <davidriley@...omium.org>,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Thierry Reding <thierry.reding@...il.com>,
	Ritesh Harjain <ritesh.harjani@...il.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv6 3/5] common: dma-mapping: Introduce common remapping
 functions

On 8/8/2014 3:45 PM, Andrew Morton wrote:
> 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).
> 
> 

Good point. I guess the best option is to increment via pfn and call
pfn_to_page. Either that or go back to slightly abusing
ioremap_page_range to remap normal memory.

Thanks,
Laura

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