Re: [PATCH v4 5/7] iommu: Add iommu_get_domain_for_dev_locked() helper

Jason Gunthorpe
2025-09-24T19:11:02Z

On Sun, Aug 31, 2025 at 04:31:57PM -0700, Nicolin Chen wrote:
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index ea2ef53bd4fef..99680cdb57265 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -2097,7 +2097,7 @@ EXPORT_SYMBOL_GPL(dma_iova_destroy);
>
> void iommu_setup_dma_ops(struct device *dev)
> {
> - struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> + struct iommu_domain *domain = iommu_get_domain_for_dev_locked(dev);

Lets have another patch to tidy this. This function can only be called on
the default_domain. We can trivally pass it in. In all three cases the
default domain was just attached to the device.

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 060ebe330ee163..93e82d5776ff57 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -620,7 +620,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list
}

if (group->default_domain)
- iommu_setup_dma_ops(dev);
+ iommu_setup_dma_ops(dev, group->default_domain);

mutex_unlock(&group->mutex);

@@ -1908,7 +1908,7 @@ static int bus_iommu_probe(const struct bus_type *bus)
return ret;
}
for_each_group_device(group, gdev)
- iommu_setup_dma_ops(gdev->dev);
+ iommu_setup_dma_ops(gdev->dev, group->default_domain);
mutex_unlock(&group->mutex);

/*
@@ -3104,7 +3104,7 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,

/* Make sure dma_ops is appropriatley set */
for_each_group_device(group, gdev)
- iommu_setup_dma_ops(gdev->dev);
+ iommu_setup_dma_ops(gdev->dev, group->default_domain);

out_unlock:
mutex_unlock(&group->mutex);

> +/* Caller must be a general/external function that isn't an IOMMU callback */
> struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)

Maybe a kdoc?

/**
* iommu_get_domain_for_dev() - Return the DMA API domain pointer
* @dev - Device to query
*
* This function can be called within a driver bound to dev. The returned
* pointer is valid for the lifetime of the bound driver.
*
* It should not be called by drivers with driver_managed_dma = true.
*/
struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)

I really wanted to say this should just always return the
default_domain, but it looks like host1x_client_iommu_detach() is the
only place outside the iommu drivers that would be unhappy with that.

Jason