[PATCH V3 6/8] arm: dma-mapping: Reset the device's dma_ops

[Russell King - ARM Linux]

On Wed, May 24, 2017 at 02:26:13PM +0300, Laurent Pinchart wrote:
> Again, the patch I propose is the simplest v4.12-rc fix I can think of, short 
> of reverting your complete IOMMU probe deferral patch series. Let's focus on 
> the v4.12-rc fix, and then discuss how to move forward in v4.13 and beyond.

Except, I don't think it fixes the problem that Sricharan is trying to
fix, namely that of DMA ops that have been setup, torn down, and are
trying to be re-setup again.  The issue here is that results in a stale
setup, because the dma_ops are left in-place from the first iommu setup,
but the iommu mapping has been disposed of.

Your patch only avoids the problem of tearing down someone else's DMA
ops.  We need a combination of both patches together.

What needs to happen for Sricharan's problem to be resolved is:

1. move all of __arm_iommu_detach_device() into arm_iommu_detach_device().
2. replace the __arm_iommu_detach_device() call in arm_teardown_iommu_dma_ops()
   with arm_iommu_detach_device().

as I don't see any need to have a different order in
arm_teardown_iommu_dma_ops().

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