linux-kernel - Re: [PATCH 1/7] dma: Take into account dma_pfn

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Message-ID: <77af42b6-d37e-c6b3-eec7-a6b9e80d10a6@arm.com>
Date:   Tue, 21 Feb 2017 13:20:21 +0000
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     kbuild-all@...org, linux@...linux.org.uk,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH 1/7] dma: Take into account dma_pfn_offset

On 21/02/17 13:07, Robin Murphy wrote:
> On 15/02/17 09:59, Vladimir Murzin wrote:
>> Even though dma-noop-ops assumes 1:1 memory mapping DMA memory range
>> can be different to RAM. For example, ARM STM32F4 MCU offers the
>> possibility to remap SDRAM from 0xc000_0000 to 0x0 to get CPU
>> performance boost, but DMA continue to see SDRAM at 0xc000_0000. This
>> difference in mapping is handled via device-tree "dma-range" property
>> which leads to dev->dma_pfn_offset is set nonzero. To handle such
>> cases take dma_pfn_offset into account.
> 
> Modulo trivial style nits (include order, line length) which I'll leave
> for others to object to if they wish, this looks correct to me.
> 
> Reviewed-by: Robin Murphy <robin.murphy@....com>

Much appreciated!

Vladimir

> 
>> Cc: Joerg Roedel <jroedel@...e.de>
>> Cc: Christian Borntraeger <borntraeger@...ibm.com>
>> Reported-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
>> Tested-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
>> Tested-by: Andras Szemzo <sza@....hu>
>> Tested-by: Alexandre TORGUE <alexandre.torgue@...com>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin@....com>
>> ---
>>  lib/dma-noop.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/dma-noop.c b/lib/dma-noop.c
>> index 3d766e7..a14eee5 100644
>> --- a/lib/dma-noop.c
>> +++ b/lib/dma-noop.c
>> @@ -7,6 +7,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/dma-mapping.h>
>>  #include <linux/scatterlist.h>
>> +#include <linux/pfn.h>
>>  
>>  static void *dma_noop_alloc(struct device *dev, size_t size,
>>  			    dma_addr_t *dma_handle, gfp_t gfp,
>> @@ -16,7 +17,8 @@ static void *dma_noop_alloc(struct device *dev, size_t size,
>>  
>>  	ret = (void *)__get_free_pages(gfp, get_order(size));
>>  	if (ret)
>> -		*dma_handle = virt_to_phys(ret);
>> +		*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
>> +
>>  	return ret;
>>  }
>>  
>> @@ -32,7 +34,7 @@ static dma_addr_t dma_noop_map_page(struct device *dev, struct page *page,
>>  				      enum dma_data_direction dir,
>>  				      unsigned long attrs)
>>  {
>> -	return page_to_phys(page) + offset;
>> +	return page_to_phys(page) + offset - PFN_PHYS(dev->dma_pfn_offset);
>>  }
>>  
>>  static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
>> @@ -47,7 +49,7 @@ static int dma_noop_map_sg(struct device *dev, struct scatterlist *sgl, int nent
>>  
>>  		BUG_ON(!sg_page(sg));
>>  		va = sg_virt(sg);
>> -		sg_dma_address(sg) = (dma_addr_t)virt_to_phys(va);
>> +		sg_dma_address(sg) = (dma_addr_t)(virt_to_phys(va) - PFN_PHYS(dev->dma_pfn_offset));
>>  		sg_dma_len(sg) = sg->length;
>>  	}
>>  
>>
> 
>