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@linux.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

On 05/06/2025 08:09, Hardik Garg wrote:
> 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@linux.microsoft.com>
> ---
> v3:
> - Added documentation for the new property in DeviceTree bindings

Please run scripts/checkpatch.pl on the patches and fix reported
warnings. After that, run also 'scripts/checkpatch.pl --strict' on the
patches and (probably) fix more warnings. Some warnings can be ignored,
especially from --strict run, but the code here looks like it needs a
fix. Feel free to get in touch if the warning is not clear.

<form letter>
Please use scripts/get_maintainers.pl to get a list of necessary people
and lists to CC. It might happen, that command when run on an older
kernel, gives you outdated entries. Therefore please be sure you base
your patches on recent Linux kernel.

Tools like b4 or scripts/get_maintainer.pl provide you proper list of
people, so fix your workflow. Tools might also fail if you work on some
ancient tree (don't, instead use mainline) or work on fork of kernel
(don't, instead use mainline). Just use b4 and everything should be
fine, although remember about `b4 prep --auto-to-cc` if you added new
patches to the patchset.

You missed at least devicetree list (maybe more), so this won't be
tested by automated tooling. Performing review on untested code might be
a waste of time.

Please kindly resend and include all necessary To/Cc entries.
</form letter>

> 
> 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


Malformed email patch. Don't use Microsoft tools to send emails... They
don't work outside of Microsoft. :/

Best regards,
Krzysztof