1What:		/sys/kernel/iommu_groups/
2Date:		May 2012
3KernelVersion:	v3.5
4Contact:	Alex Williamson <[email protected]>
5Description:	/sys/kernel/iommu_groups/ contains a number of sub-
6		directories, each representing an IOMMU group.  The
7		name of the sub-directory matches the iommu_group_id()
8		for the group, which is an integer value.  Within each
9		subdirectory is another directory named "devices" with
10		links to the sysfs devices contained in this group.
11		The group directory also optionally contains a "name"
12		file if the IOMMU driver has chosen to register a more
13		common name for the group.
14Users:
15
16What:		/sys/kernel/iommu_groups/reserved_regions
17Date: 		January 2017
18KernelVersion:  v4.11
19Contact: 	Eric Auger <[email protected]>
20Description:    /sys/kernel/iommu_groups/reserved_regions list IOVA
21		regions that are reserved. Not necessarily all
22		reserved regions are listed. This is typically used to
23		output direct-mapped, MSI, non mappable regions. Each
24		region is described on a single line: the 1st field is
25		the base IOVA, the second is the end IOVA and the third
26		field describes the type of the region.
27
28What:		/sys/kernel/iommu_groups/reserved_regions
29Date: 		June 2019
30KernelVersion:  v5.3
31Contact: 	Eric Auger <[email protected]>
32Description:    In case an RMRR is used only by graphics or USB devices
33		it is now exposed as "direct-relaxable" instead of "direct".
34		In device assignment use case, for instance, those RMRR
35		are considered to be relaxable and safe.
36
37What:		/sys/kernel/iommu_groups/<grp_id>/type
38Date:		November 2020
39KernelVersion:	v5.11
40Contact:	Sai Praneeth Prakhya <[email protected]>
41Description:	/sys/kernel/iommu_groups/<grp_id>/type shows the type of default
42		domain in use by iommu for this group. See include/linux/iommu.h
43		for possible values. A privileged user could request kernel to
44		change the group type by writing to this file. Presently, only
45		three types of request are supported:
46		1. DMA: All the DMA transactions from the device in this group
47			are translated by the iommu.
48		2. identity: All the DMA transactions from the device in this
49			     group are *not* translated by the iommu.
50		3. auto: Change to the type the device was booted with.
51		Note:
52		-----
53		The default domain type of a group may be modified only when
54		1. The group has *only* one device
55		2. The device in the group is not bound to any device driver.
56		   So, the users must unbind the appropriate driver before
57		   changing the default domain type.
58		Caution:
59		--------
60		Unbinding a device driver will take away the driver's control
61		over the device and if done on devices that host root file
62		system could lead to catastrophic effects (the users might
63		need to reboot the machine to get it to normal state). So, it's
64		expected that the users understand what they're doing.
65