linux-kernel - Re: [PATCH v2 3/4] iommu/dma-iommu: Use the dev->coherent_dma

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Message-ID: <20190430113253.GA23210@infradead.org>
Date:   Tue, 30 Apr 2019 04:32:53 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Tom Murphy <tmurphy@...sta.com>,
        iommu@...ts.linux-foundation.org, Heiko Stuebner <heiko@...ech.de>,
        Will Deacon <will.deacon@....com>,
        David Brown <david.brown@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-s390@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-rockchip@...ts.infradead.org, Kukjin Kim <kgene@...nel.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Andy Gross <andy.gross@...aro.org>,
        linux-tegra@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        murphyt7@....ie, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2 3/4] iommu/dma-iommu: Use the dev->coherent_dma_mask

On Tue, Apr 30, 2019 at 12:27:02PM +0100, Robin Murphy wrote:
> > Hmm, I don't think we need the DMA mask for the MSI mapping, this
> > should probably always use a 64-bit mask.
> 
> If that were true then we wouldn't need DMA masks for regular mappings
> either. If we have to map the MSI doorbell at all, then we certainly have to
> place it at an IOVA that the relevant device is actually capable of
> addressing.

Well, as shown by the patch below we don't even look at the DMA mask
for the MSI page - we just allocate from bottom to top.