linux-kernel - [PATCH v4 2/2] vmbus: retrieve connection-id from DeviceTree

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Message-Id: <1750374395-14615-3-git-send-email-hargar@linux.microsoft.com>
Date: Thu, 19 Jun 2025 16:06:35 -0700
From: Hardik Garg <hargar@...ux.microsoft.com>
To: kys@...rosoft.com,
	haiyangz@...rosoft.com,
	wei.liu@...nel.org,
	decui@...rosoft.com,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org
Cc: devicetree@...r.kernel.org,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	ssengar@...ux.microsoft.com,
	hargar@...rosoft.com,
	apais@...rosoft.com,
	Hardik Garg <hargar@...ux.microsoft.com>
Subject: [PATCH v4 2/2] 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: https://lore.kernel.org/all/6a92ca86-ad6b-4d49-af6e-1ed7651b8ab8@linux.microsoft.com
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
---
 drivers/hv/connection.c |  6 ++++--
 drivers/hv/vmbus_drv.c  | 13 +++++++++++++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index be490c598785..15d2b652783d 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -99,11 +99,13 @@ 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
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index c236081d0a87..b78d5499e4bc 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