[PATCH 1/2] iommu: Add static iommu_ops->release_domain

[Lu Baolu]

The current device_release callback for individual iommu drivers does the
following:

1) Silent IOMMU DMA translation: It detaches any existing domain from the
   device and puts it into a blocking state (some drivers might use the
   identity state).
2) Resource release: It releases resources allocated during the
   device_probe callback and restores the device to its pre-probe state.

Step 1 is challenging for individual iommu drivers because each must check
if a domain is already attached to the device. Additionally, if a deferred
attach never occurred, the device_release should avoid modifying hardware
configuration regardless of the reason for its call.

To simplify this process, introduce a static release_domain within the
iommu_ops structure. It can be either a blocking or identity domain
depending on the iommu hardware. The iommu core will decide whether to
attach this domain before the device_release callback, eliminating the
need for repetitive code in various drivers.

Consequently, the device_release callback can focus solely on the opposite
operations of device_probe, including releasing all resources allocated
during that callback.

Co-developed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 include/linux/iommu.h |  1 +
 drivers/iommu/iommu.c | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index de839fd01bb8..e3d9365b0fa9 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -585,6 +585,7 @@ struct iommu_ops {
 	struct module *owner;
 	struct iommu_domain *identity_domain;
 	struct iommu_domain *blocked_domain;
+	struct iommu_domain *release_domain;
 	struct iommu_domain *default_domain;
 };
 
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 210dc7b4c8cf..fb06c3f47320 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -459,6 +459,18 @@ static void iommu_deinit_device(struct device *dev)
 
 	iommu_device_unlink(dev->iommu->iommu_dev, dev);
 
+	/*
+	 * If the iommu driver provides release_domain then the core code
+	 * ensures that domain is attached prior to calling release_device.
+	 * Drivers can use this to enforce a translation on the idle iommu.
+	 * Usually the global static blocked_domain is a good choice.
+	 *
+	 * Anyway, if a deferred attach never happened then the release
+	 * should still avoid touching any hardware configuration either.
+	 */
+	if (!dev->iommu->attach_deferred && ops->release_domain)
+		ops->release_domain->ops->attach_dev(ops->release_domain, dev);
+
 	/*
 	 * release_device() must stop using any attached domain on the device.
 	 * If there are still other devices in the group they are not effected
-- 
2.34.1