Re: [Nouveau] [PATCH v4 2/6] drm/nouveau: map pages using DMA API on platform devices

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jul 08, 2014 at 05:25:57PM +0900, Alexandre Courbot wrote:
> page_to_phys() is not the correct way to obtain the DMA address of a
> buffer on a non-PCI system. Use the DMA API functions for this, which
> are portable and will allow us to use other DMA API functions for
> buffer synchronization.
> 
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
>  drivers/gpu/drm/nouveau/core/engine/device/base.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/core/engine/device/base.c b/drivers/gpu/drm/nouveau/core/engine/device/base.c
> index 18c8c7245b73..e4e9e64988fe 100644
> --- a/drivers/gpu/drm/nouveau/core/engine/device/base.c
> +++ b/drivers/gpu/drm/nouveau/core/engine/device/base.c
> @@ -489,7 +489,10 @@ nv_device_map_page(struct nouveau_device *device, struct page *page)
>  		if (pci_dma_mapping_error(device->pdev, ret))
>  			ret = 0;
>  	} else {
> -		ret = page_to_phys(page);
> +		ret = dma_map_page(&device->platformdev->dev, page, 0,
> +				   PAGE_SIZE, DMA_BIDIRECTIONAL);
> +		if (dma_mapping_error(&device->platformdev->dev, ret))
> +			ret = 0;
>  	}
>  
>  	return ret;
> @@ -501,6 +504,9 @@ nv_device_unmap_page(struct nouveau_device *device, dma_addr_t addr)
>  	if (nv_device_is_pci(device))
>  		pci_unmap_page(device->pdev, addr, PAGE_SIZE,
>  			       PCI_DMA_BIDIRECTIONAL);

pci_map/unmap alias to dma_unmap/map when called on the underlying struct
device embedded in pci_device (like for platform drivers). Dunno whether
it's worth to track a pointer to the struct device directly and always
call dma_unmap/map.

Just drive-by comment since I'm interested in how you solve this - i915
has similar fun with buffer sharing and coherent and non-coherent
platforms. Although we don't have fun with pci and non-pci based
platforms.
-Daniel

> +	else
> +		dma_unmap_page(&device->platformdev->dev, addr,
> +			       PAGE_SIZE, DMA_BIDIRECTIONAL);
>  }
>  
>  int
> -- 
> 2.0.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch