linux-kernel - [PATCH v9 4/4] iommu: Document usage of "/sys/kernel/iommu_groups/<grp

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Message-Id: <20201121135620.3496419-5-baolu.lu@linux.intel.com>
Date:   Sat, 21 Nov 2020 21:56:20 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>
Cc:     Ashok Raj <ashok.raj@...el.com>, Christoph Hellwig <hch@....de>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        Will Deacon <will.deacon@....com>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: [PATCH v9 4/4] iommu: Document usage of "/sys/kernel/iommu_groups/<grp_id>/type" file

From: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.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@....de>
Cc: Joerg Roedel <joro@...tes.org>
Cc: Ashok Raj <ashok.raj@...el.com>
Cc: Will Deacon <will.deacon@....com>
Cc: Sohil Mehta <sohil.mehta@...el.com>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
---
 .../ABI/testing/sysfs-kernel-iommu_groups     | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
index 017f5bc3920c..407b1628d7fd 100644
--- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups
+++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
@@ -33,3 +33,32 @@ 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:		November 2020
+KernelVersion:	v5.11
+Contact:	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
+Description:	/sys/kernel/iommu_groups/<grp_id>/type shows the type of default
+		domain in use by iommu for this group. See include/linux/iommu.h
+		for possible values. A privileged user could request kernel to
+		change the group type by writing to this file. Presently, only
+		three types of request 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.
+		Note:
+		-----
+		The default domain type of a group may 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 users must unbind the appropriate driver before
+		   changing 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 users might
+		need to reboot the machine to get it to normal state). So, it's
+		expected that the users understand what they're doing.
-- 
2.25.1