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

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Message-ID:
 <SN6PR02MB4157F2C0674B85C7206E6047D47CA@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Fri, 20 Jun 2025 02:36:39 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Hardik Garg <hargar@...ux.microsoft.com>, "kys@...rosoft.com"
	<kys@...rosoft.com>, "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>, "decui@...rosoft.com"
	<decui@...rosoft.com>, "robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>, "conor+dt@...nel.org"
	<conor+dt@...nel.org>
CC: "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
	"hargar@...rosoft.com" <hargar@...rosoft.com>, "apais@...rosoft.com"
	<apais@...rosoft.com>
Subject: RE: [PATCH v4 2/2] vmbus: retrieve connection-id from DeviceTree

From: Hardik Garg <hargar@...ux.microsoft.com> Sent: Thursday, June 19, 2025 4:07 PM
> 

For the patch "Subject:" line, prefer prefix "Drivers: hv: vmbus:" to be consistent
historical precedent. We haven't always been consistent with that precedent,
but I try to call it out when I have the opportunity. :-)  If you look at the commit
log for drivers/hv, you'll see that prefix fairly often, though sometimes
shortened to just "Drivers: hv:" when the change is more generically for
Hyper-V and not specifically VMBus.

> 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".

Avoid wording like "this patch" in commit messages. Commit messages should
be in imperative mood.  So something like:

The connection-id determines which hypervisor communication channel the
guest should use to talk to the VMBus host. Add steps 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;

Indentation problem here. Should be a full tab, not 4 spaces.

> +	}
> +
>  	ret = of_range_parser_init(&parser, np);
>  	if (ret)
>  		return ret;
> --
> 2.40.4
>