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From: Sai Praneeth Prakhya <>
Cc: Ashok Raj <>,
	Will Deacon <>,
	Robin Murphy <>,
	Christoph Hellwig <>
Subject: [PATCH V4 3/3] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file
Date: Thu,  4 Jun 2020 18:32:08 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

The default domain type of an iommu group can be changed by writing to
"/sys/kernel/iommu_groups/<grp_id>/type" file. Hence, document it's usage
and more importantly spell out its limitations.

Cc: Christoph Hellwig <>
Cc: Joerg Roedel <>
Cc: Ashok Raj <>
Cc: Will Deacon <>
Cc: Lu Baolu <>
Cc: Sohil Mehta <>
Cc: Robin Murphy <>
Cc: Jacob Pan <>
Signed-off-by: Sai Praneeth Prakhya <>
 .../ABI/testing/sysfs-kernel-iommu_groups     | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
index 017f5bc3920c..a498daffeb0c 100644
--- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups
+++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
@@ -33,3 +33,33 @@ Description:    In case an RMRR is used only by graphics or USB devices
 		it is now exposed as "direct-relaxable" instead of "direct".
 		In device assignment use case, for instance, those RMRR
 		are considered to be relaxable and safe.
+What:		/sys/kernel/iommu_groups/<grp_id>/type
+Date:		June 2020
+KernelVersion:	v5.8
+Contact:	Sai Praneeth Prakhya <>
+Description:	Let the user know the type of default domain in use by iommu
+		for this group. A privileged user could request kernel to change
+		the group type by writing to this file. Presently, only three
+		types are supported
+		1. DMA: All the DMA transactions from the device in this group
+			are translated by the iommu.
+		2. identity: All the DMA transactions from the device in this
+			     group are *not* translated by the iommu.
+		3. auto: Change to the type the device was booted with. When the
+			 user reads the file he would never see "auto". This is
+			 just a write only value.
+		Note:
+		-----
+		A group type could be modified only when
+		1. The group has *only* one device
+		2. The device in the group is not bound to any device driver.
+		   So, the user must first unbind the appropriate driver and
+		   then change the default domain type.
+		Caution:
+		--------
+		Unbinding a device driver will take away the driver's control
+		over the device and if done on devices that host root file
+		system could lead to catastrophic effects (the user might
+		need to reboot the machine to get it to normal state). So, it's
+		expected that the user understands what he is doing.

iommu mailing list

  parent reply	other threads:[~2020-06-05  1:35 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-05  1:32 [PATCH V4 0/3] iommu: Add support to change default domain of an iommu group Sai Praneeth Prakhya
2020-06-05  1:32 ` [PATCH V4 1/3] " Sai Praneeth Prakhya
2020-06-08  1:49   ` Lu Baolu
2020-06-30  9:16   ` Joerg Roedel
2020-07-01  3:04     ` Prakhya, Sai Praneeth
2020-07-14 18:23       ` Prakhya, Sai Praneeth
2020-07-22 13:52         ` Joerg Roedel
2020-07-22 17:14           ` Prakhya, Sai Praneeth
2020-06-05  1:32 ` [PATCH V4 2/3] iommu: Take lock before reading iommu group default domain type Sai Praneeth Prakhya
2020-06-08  1:50   ` Lu Baolu
2020-06-05  1:32 ` Sai Praneeth Prakhya [this message]
2020-06-08  1:50   ` [PATCH V4 3/3] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file Lu Baolu
2020-06-26 21:34 ` [PATCH V4 0/3] iommu: Add support to change default domain of an iommu group Prakhya, Sai Praneeth

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