[RFC PATCH v5 1/7] dma: Take into account dma_pfn_offset

[Joerg Roedel]

On Wed, Jan 18, 2017 at 11:13:17AM +0000, 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.
> 
> Cc: Joerg Roedel <jroedel at suse.de>
> Cc: Christian Borntraeger <borntraeger at de.ibm.com>
> Reported-by: Benjamin Gaignard <benjamin.gaignard at linaro.org>
> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.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);
> +

If you need to do a '-' operation here, the offset is basically a
cpu_pfn_offset for the device. Is that correct?


	Joerg