linux-kernel - Re: [PATCH v3 0/6] Prerequisites for NXP LS104xA SMMU enablement

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Date:   Fri, 31 May 2019 10:08:04 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        David Miller <davem@...emloft.net>, madalin.bucur@....com,
        netdev@...r.kernel.org, roy.pledge@....com,
        linux-kernel@...r.kernel.org, leoyang.li@....com,
        Joakim.Tjernlund@...inera.com, iommu@...ts.linux-foundation.org,
        camelia.groza@....com, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/6] Prerequisites for NXP LS104xA SMMU enablement

On Fri, May 31, 2019 at 06:03:30PM +0100, Robin Murphy wrote:
> > The thing needs to be completely redone as it abuses parts of the
> > iommu API in a completely unacceptable way.
> 
> `git grep iommu_iova_to_phys drivers/{crypto,gpu,net}`
> 
> :(
> 
> I guess one alternative is for the offending drivers to maintain their own
> lookup tables of mapped DMA addresses - I think at least some of these
> things allow storing some kind of token in a descriptor, which even if it's
> not big enough for a virtual address might be sufficient for an index.

Well, we'll at least need DMA API wrappers that work on the dma addr
only and hide this madness underneath.  And then tell if an given device
supports this and fail the probe otherwise.