linux-kernel - Re: [PATCH] dma-direct: Export dma_direct_alloc() and dma_direct

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Message-ID: <20190205175611.GA7052@ulmo>
Date:   Tue, 5 Feb 2019 18:56:11 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-direct: Export dma_direct_alloc() and
 dma_direct_free()

On Tue, Feb 05, 2019 at 05:38:37PM +0100, Christoph Hellwig wrote:
> On Tue, Feb 05, 2019 at 05:20:57PM +0100, Thierry Reding wrote:
> > The problem is that if I use dma_alloc_coherent(), then the memory will
> > already be mapped via the SMMU at that point and then the driver, not
> > knowing that memory has already been mapped, will attempt to map an IOVA
> > which will cause an SMMU fault when the host1x tries to access the
> > memory.
> > 
> > I didn't find an equivalent to arm_iommu_detach_device() for non-ARM,
> > but then stumbled across this and thought it was rather convenient for
> > these cases. If there's a better way to deal with this situation, I'd be
> > happy to do so.
> 
> So you basically do a dma_direct_alloc + iommu_map?  Can you send me
> a pointer to your code?  Maybe we need to add a proper IOMMU-layer
> API for that.

Sure, here you go:

	https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/host1x/cdma.c#n106

Thierry

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