linux-kernel - Re: [PATCH v4 5/7] iommu: Add iommu_get_domain_for_dev

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Message-ID: <20250924191055.GJ2617119@nvidia.com>
Date: Wed, 24 Sep 2025 16:10:55 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
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Subject: Re: [PATCH v4 5/7] iommu: Add iommu_get_domain_for_dev_locked()
 helper

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