From: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
To: iommu@lists.linux-foundation.org
Cc: Ashok Raj <ashok.raj@intel.com>,
Will Deacon <will.deacon@arm.com>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>
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: <24102f22824b26cf4fa6ec1c84d176110b21c574.1591290586.git.sai.praneeth.prakhya@intel.com> (raw)
In-Reply-To: <cover.1591290586.git.sai.praneeth.prakhya@intel.com>
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 <hch@lst.de>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
---
.../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 <sai.praneeth.prakhya@intel.com>
+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.
--
2.19.1
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev 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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