linux-kernel - [PATCH v3] vmbus: retrieve connection-id from DeviceTree

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Message-ID: <6a92ca86-ad6b-4d49-af6e-1ed7651b8ab8@linux.microsoft.com>
Date: Wed, 4 Jun 2025 23:09:31 -0700
From: Hardik Garg <hargar@...ux.microsoft.com>
To: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
 decui@...rosoft.com, ssengar@...rosoft.com
Cc: romank@...ux.microsoft.com, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...nel.org, apais@...rosoft.com
Subject: [PATCH v3] vmbus: retrieve connection-id from DeviceTree

The connection-id determines which hypervisor communication channel the
guest should use to talk to the VMBus host. This patch adds support to
read this value from the DeviceTree where it exists as a property under
the vmbus node with the compatible ID "microsoft,message-connection-id".
The property name follows the format <vendor>,<field> where
"vendor": "microsoft" and "field": "message-connection-id"

Reading from DeviceTree allows platforms to specify their preferred
communication channel, making it more flexible. If the property is
not found in the DeviceTree, use the default connection ID
(VMBUS_MESSAGE_CONNECTION_ID or VMBUS_MESSAGE_CONNECTION_ID_4
based on protocol version).

Signed-off-by: Hardik Garg <hargar@...ux.microsoft.com>
---
v3:
- Added documentation for the new property in DeviceTree bindings

v2: 
https://lore.kernel.org/all/096edaf7-cc90-42b6-aff4-c5f088574e1e@linux.microsoft.com/

v1: 
https://lore.kernel.org/all/6acee4bf-cb04-43b9-9476-e8d811d26dfd@linux.microsoft.com/
---
  .../devicetree/bindings/bus/microsoft,vmbus.yaml    |  8 ++++++++
  drivers/hv/connection.c                             |  6 ++++--
  drivers/hv/vmbus_drv.c                              | 13 +++++++++++++
  3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/bus/microsoft,vmbus.yaml 
b/Documentation/devicetree/bindings/bus/microsoft,vmbus.yaml
index 0bea4f5287ce..729ca6defec6 100644
--- a/Documentation/devicetree/bindings/bus/microsoft,vmbus.yaml
+++ b/Documentation/devicetree/bindings/bus/microsoft,vmbus.yaml
@@ -17,6 +17,14 @@ properties:
    compatible:
      const: microsoft,vmbus

+  microsoft,message-connection-id:
+    description:
+      VMBus message connection ID to be used for communication between 
host and
+      guest. If not specified, defaults to 
VMBUS_MESSAGE_CONNECTION_ID_4 for
+      protocol version VERSION_WIN10_V5 and above, or 
VMBUS_MESSAGE_CONNECTION_ID
+      for older versions.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
    ranges: true

    '#address-cells':
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index be490c598785..e0f38d799d06 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -99,12 +99,14 @@ int vmbus_negotiate_version(struct 
vmbus_channel_msginfo *msginfo, u32 version)
      if (version >= VERSION_WIN10_V5) {
          msg->msg_sint = VMBUS_MESSAGE_SINT;
          msg->msg_vtl = ms_hyperv.vtl;
-        vmbus_connection.msg_conn_id = VMBUS_MESSAGE_CONNECTION_ID_4;
      } else {
          msg->interrupt_page = virt_to_phys(vmbus_connection.int_page);
-        vmbus_connection.msg_conn_id = VMBUS_MESSAGE_CONNECTION_ID;
      }

+    /* Set default connection ID if not provided via DeviceTree */
+    if (!vmbus_connection.msg_conn_id)
+        vmbus_connection.msg_conn_id = (version >= VERSION_WIN10_V5) ?
+            VMBUS_MESSAGE_CONNECTION_ID_4 : VMBUS_MESSAGE_CONNECTION_ID;
      /*
       * shared_gpa_boundary is zero in non-SNP VMs, so it's safe to always
       * bitwise OR it
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index c236081d0a87..d14d286671cc 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2541,10 +2541,23 @@ static int vmbus_device_add(struct 
platform_device *pdev)
      struct of_range range;
      struct of_range_parser parser;
      struct device_node *np = pdev->dev.of_node;
+    unsigned int conn_id;
      int ret;

      vmbus_root_device = &pdev->dev;

+    /*
+     * Read connection ID from DeviceTree. The property name follows the
+     * format <vendor>,<field> where:
+     * - vendor: "microsoft"
+     * - field: "message-connection-id"
+     */
+    ret = of_property_read_u32(np, "microsoft,message-connection-id", 
&conn_id);
+    if (!ret) {
+        pr_info("VMBus message connection ID: %u\n", conn_id);
+        vmbus_connection.msg_conn_id = conn_id;
+    }
+
      ret = of_range_parser_init(&parser, np);
      if (ret)
          return ret;
-- 
2.40.4