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

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Date:   Tue, 21 Feb 2017 13:07:38 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Vladimir Murzin <vladimir.murzin@....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 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>

> 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;
>  	}
>  
>