On 30/05/18 15:06, Thierry Reding wrote:
From: Thierry Reding <tred...@nvidia.com>

Instead of setting the DMA ops pointer to NULL, set the correct,
non-IOMMU ops depending on the device's coherency setting.

It looks like it's probably been 4 or 5 years since that became subtly wrong by virtue of the landscape changing around it, but it's clearly not enough of a problem to consider stable backports :)

Reviewed-by: Robin Murphy <robin.mur...@arm.com>

Signed-off-by: Thierry Reding <tred...@nvidia.com>
---
Changes in v4:
- new patch to fix existing arm_iommu_detach_device() to do what we need

  arch/arm/mm/dma-mapping.c | 12 ++++++------
  1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index af27f1c22d93..87a0037574e4 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1151,6 +1151,11 @@ int arm_dma_supported(struct device *dev, u64 mask)
        return __dma_supported(dev, mask, false);
  }
+static const struct dma_map_ops *arm_get_dma_map_ops(bool coherent)
+{
+       return coherent ? &arm_coherent_dma_ops : &arm_dma_ops;
+}
+
  #ifdef CONFIG_ARM_DMA_USE_IOMMU
static int __dma_info_to_prot(enum dma_data_direction dir, unsigned long attrs)
@@ -2296,7 +2301,7 @@ void arm_iommu_detach_device(struct device *dev)
        iommu_detach_device(mapping->domain, dev);
        kref_put(&mapping->kref, release_iommu_mapping);
        to_dma_iommu_mapping(dev) = NULL;
-       set_dma_ops(dev, NULL);
+       set_dma_ops(dev, arm_get_dma_map_ops(dev->archdata.dma_coherent));
pr_debug("Detached IOMMU controller from %s device.\n", dev_name(dev));
  }
@@ -2357,11 +2362,6 @@ static void arm_teardown_iommu_dma_ops(struct device 
*dev) { }
#endif /* CONFIG_ARM_DMA_USE_IOMMU */ -static const struct dma_map_ops *arm_get_dma_map_ops(bool coherent)
-{
-       return coherent ? &arm_coherent_dma_ops : &arm_dma_ops;
-}
-
  void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
                        const struct iommu_ops *iommu, bool coherent)
  {

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