linux-kernel - Re: [PATCH 4/9] iommu/dma-iommu: Add iommu_dma_map_page

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Date:   Sun, 14 Apr 2019 23:33:17 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Tom Murphy <tmurphy@...sta.com>
Cc:     iommu@...ts.linux-foundation.org, Heiko Stuebner <heiko@...ech.de>,
        Will Deacon <will.deacon@....com>,
        David Brown <david.brown@...aro.org>,
        linux-samsung-soc@...r.kernel.org, dima@...sta.com,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-rockchip@...ts.infradead.org, Kukjin Kim <kgene@...nel.org>,
        Andy Gross <andy.gross@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        murphyt7@....ie, Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 4/9] iommu/dma-iommu: Add iommu_dma_map_page_coherent

> @@ -693,7 +694,19 @@ dma_addr_t iommu_dma_map_page(struct device *dev, struct page *page,
>  		unsigned long offset, size_t size, int prot)
>  {
>  	return __iommu_dma_map(dev, page_to_phys(page) + offset, size, prot,
> -			iommu_get_dma_domain(dev));
> +			iommu_get_dma_domain(dev), dma_get_mask(dev));
> +}
> +
> +dma_addr_t iommu_dma_map_page_coherent(struct device *dev, struct page *page,
> +		unsigned long offset, size_t size, int prot)
> +{

Note that my tree pointed to above removes the iommu_dma_map_page
wrapper.  I think for the coherent mappign we should also just
call __iommu_dma_map directly and not introduce another wrapper.

> +	dma_addr_t dma_mask = dev->coherent_dma_mask;
> +
> +	if (!dma_mask)
> +		dma_mask = dma_get_mask(dev);
> +
> +	return __iommu_dma_map(dev, page_to_phys(page) + offset, size, prot,
> +			iommu_get_dma_domain(dev), dma_mask);
>  }

In the DMA API there is no fallback when the coherent_dma_mask is not
set.  While various bits of legacy code do that we should not copy it
to new code.