Hi Stefano,
On 24/05/2024 23:16, Stefano Stabellini wrote:
From: Vikram Garhwal <fnu.vik...@xilinx.com>
Signed-off-by: Vikram Garhwal <fnu.vik...@xilinx.com>
Signed-off-by: Stefano Stabellini <stefano.stabell...@xilinx.com>
Signed-off-by: Henry Wang <xin.wa...@amd.com>
---
docs/misc/arm/overlay.txt | 82 +++++++++++++++++++++++++++++++++++++++
1 file changed, 82 insertions(+)
create mode 100644 docs/misc/arm/overlay.txt
diff --git a/docs/misc/arm/overlay.txt b/docs/misc/arm/overlay.txt
new file mode 100644
index 0000000000..ef3ef792f7
--- /dev/null
+++ b/docs/misc/arm/overlay.txt
@@ -0,0 +1,82 @@
+# Device Tree Overlays support in Xen
+
+Xen experimentally supports dynamic device assignment to running
+domains, i.e. adding/removing nodes (using .dtbo) to/from Xen device
+tree, and attaching them to a running domain with given $domid.
+
+Dynamic node assignment works in two steps:
+
+## Add/Remove device tree overlay to/from Xen device tree
+
+1. Xen tools check the dtbo given and parse all other user provided arguments
+2. Xen tools pass the dtbo to Xen hypervisor via hypercall.
+3. Xen hypervisor applies/removes the dtbo to/from Xen device tree.
+
+## Attach device from the DT overlay to domain
+
+1. Xen tools check the dtbo given and parse all other user provided arguments
+2. Xen tools pass the dtbo to Xen hypervisor via hypercall.
+3. Xen hypervisor attach the device to the user-provided $domid by
+ mapping node resources in the DT overlay.
+
+# Examples
+
+Here are a few examples on how to use it.
+
+## Dom0 device add
+
+For assigning a device tree overlay to Dom0, user should firstly properly
+prepare the DT overlay. More information about device tree overlays can be
+found in [1]. Then, in Dom0, enter the following:
+
+ (dom0) xl dt-overlay add overlay.dtbo
+
+This will allocate the devices mentioned in overlay.dtbo to Xen device tree.
+
+To assign the newly added device from the dtbo to Dom0:
+
+ (dom0) xl dt-overlay attach overlay.dtbo 0
+
+Next, if the user wants to add the same device tree overlay to dom0
+Linux, execute the following:
+
+ (dom0) mkdir -p /sys/kernel/config/device-tree/overlays/new_overlay
+ (dom0) cat overlay.dtbo >
/sys/kernel/config/device-tree/overlays/new_overlay/dtbo
+
+Finally if needed, the relevant Linux kernel drive can be loaded using:
+
+ (dom0) modprobe module_name.ko
+
+## DomU device add/remove
+
+All the nodes in dtbo will be assigned to one domain. The user will need
+to prepare a different dtbo for the domU. For example, the
+`interrupt-parent` property of the DomU overlay should be changed to the
+Xen hardcoded value `0xfde8` and the xen,reg property should be added to
+specify the address mappings. If the domain is not 1:1 mapped, xen,reg
+must be present. See the xen,reg format description in
+docs/misc/arm/passthrough.txt. Below assumes the properly written DomU
+dtbo is `overlay_domu.dtbo`.
+
+You need to set the `passthrough` property in the xl config file if you
s/You need/The user needs/ to match the rest of the documentation.
With that addresed:
Reviewed-by: Julien Grall <jgr...@amazon.com>
Cheers,
--
Julien Grall
