This callback requests the driver to create only a __IOMMU_DOMAIN_PAGING
domain, so it saves a few lines in a lot of drivers needlessly checking
the type.

More critically, this allows us to sweep out all the
IOMMU_DOMAIN_UNMANAGED and IOMMU_DOMAIN_DMA checks from a lot of the
drivers, simplifying what is going on in the code and ultimately removing
the now-unused special cases in drivers where they did not support
IOMMU_DOMAIN_DMA.

domain_alloc_paging() should return a struct iommu_domain that is
functionally compatible with ARM_DMA_USE_IOMMU, dma-iommu.c and iommufd.

Be forwards looking and pass in a 'struct device *' argument. We can
provide this when allocating the default_domain. No drivers will look at
this.

Signed-off-by: Jason Gunthorpe <j...@nvidia.com>
---
 drivers/iommu/iommu.c | 18 +++++++++++++++---
 include/linux/iommu.h |  3 +++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index c4cac1dcf80610..15aa51c356bd74 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1995,14 +1995,25 @@ void iommu_set_fault_handler(struct iommu_domain 
*domain,
 EXPORT_SYMBOL_GPL(iommu_set_fault_handler);
 
 static struct iommu_domain *__iommu_domain_alloc(const struct iommu_ops *ops,
+                                                struct device *dev,
                                                 unsigned int type)
 {
        struct iommu_domain *domain;
 
        if (type == IOMMU_DOMAIN_IDENTITY && ops->identity_domain)
                return ops->identity_domain;
+       else if ((type == IOMMU_DOMAIN_UNMANAGED || type == IOMMU_DOMAIN_DMA) &&
+                ops->domain_alloc_paging) {
+               /*
+                * For now exclude DMA_FQ since it is still a driver policy
+                * decision through domain_alloc() if we can use FQ mode.
+                */
+               domain = ops->domain_alloc_paging(dev);
+       } else if (ops->domain_alloc)
+               domain = ops->domain_alloc(type);
+       else
+               return NULL;
 
-       domain = ops->domain_alloc(type);
        if (!domain)
                return NULL;
 
@@ -2033,14 +2044,15 @@ __iommu_group_domain_alloc(struct iommu_group *group, 
unsigned int type)
 
        lockdep_assert_held(&group->mutex);
 
-       return __iommu_domain_alloc(dev_iommu_ops(dev), type);
+       return __iommu_domain_alloc(dev_iommu_ops(dev), dev, type);
 }
 
 struct iommu_domain *iommu_domain_alloc(const struct bus_type *bus)
 {
        if (bus == NULL || bus->iommu_ops == NULL)
                return NULL;
-       return __iommu_domain_alloc(bus->iommu_ops, IOMMU_DOMAIN_UNMANAGED);
+       return __iommu_domain_alloc(bus->iommu_ops, NULL,
+                                   IOMMU_DOMAIN_UNMANAGED);
 }
 EXPORT_SYMBOL_GPL(iommu_domain_alloc);
 
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 387746f8273c99..18b0df42cc80d1 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -227,6 +227,8 @@ struct iommu_iotlb_gather {
  * struct iommu_ops - iommu ops and capabilities
  * @capable: check capability
  * @domain_alloc: allocate iommu domain
+ * @domain_alloc_paging: Allocate an iommu_domain that can be used for
+ *                       UNMANAGED, DMA, and DMA_FQ domain types.
  * @probe_device: Add device to iommu driver handling
  * @release_device: Remove device from iommu driver handling
  * @probe_finalize: Do final setup work after the device is added to an IOMMU
@@ -258,6 +260,7 @@ struct iommu_ops {
 
        /* Domain allocation and freeing by the iommu driver */
        struct iommu_domain *(*domain_alloc)(unsigned iommu_domain_type);
+       struct iommu_domain *(*domain_alloc_paging)(struct device *dev);
 
        struct iommu_device *(*probe_device)(struct device *dev);
        void (*release_device)(struct device *dev);
-- 
2.40.1

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