Hi Will,
On 11/18/20 9:51 PM, Will Deacon wrote:
On Fri, Sep 25, 2020 at 12:06:20PM -0700, Ashok Raj wrote:
From: Sai Praneeth Prakhya <[email protected]>
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 <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Ashok Raj <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Lu Baolu <[email protected]>
Cc: Sohil Mehta <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Jacob Pan <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Signed-off-by: Sai Praneeth Prakhya <[email protected]>
---
.../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..effde9d23f4f 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: September 2020
+KernelVersion: v5.10
^^ Please can you update these two lines?
Sure.
+Contact: Sai Praneeth Prakhya <[email protected]>
+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
Can we avoid assuming gender here and just use "they" instead of "he", please?
Same thing for the "Caution" note below.
Yes, absolutely.
+ just a write only value.
I can't figure out from this description what string is returned to
userspace in the case that the group is configured as blocked or unmanaged.
This series only enables switching a default domain in use between DMA
and IDENTITY. Other cases will result in write failures.
+ Note:
+ -----
+ A group type could be modified only when
s/could be/may be/
+ 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.
Thanks,
Will
Best regards,
baolu
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