From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Wilk <konrad.wilk-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v5 04/13] DMA-API: Introduce dma_(un)map_peer_resource
Date: Tue, 18 Aug 2015 16:26:09 -0700 (PDT)
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> +#ifdef CONFIG_HAS_DMA_P2P
> +static inline dma_peer_addr_t dma_map_peer_resource_attrs(struct
> device *dev,
> +							  struct device *peer,
> +							  struct resource *res,
> +							  size_t offset,
> +							  size_t size,
> +							  enum dma_data_direction dir,
> +							  struct dma_attrs *attrs)
> +{
> +	struct dma_map_ops *ops = get_dma_ops(dev);
> +	dma_peer_addr_t addr;
> +
> +	BUG_ON(!valid_dma_direction(dir));
> +	BUG_ON(ops->map_peer_resource == NULL);
> +	addr = ops->map_peer_resource(dev, peer, res, offset, size, dir,
> +				      attrs);
> +	debug_dma_map_peer_resource(dev, peer, res, offset, size, dir,
> addr);
> +
> +	return addr;
> +

With those 'BUG_ON' you need to make sure that every dma_map_ops has
this implemented. That means the calgary_dma_ops, gart_dma_ops, swiotlb_dma_ops,
and xen_swiotlb_dma_ops MUST have something implemented.

Please keep in mind that on one can do 'iommu=soft swiotbl=force' on the
command line which will force the IOMMUs to be ignored and only the
SWIOTLB code will be used.