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

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Message-ID: <20250620-miniature-wisteria-moose-8d8cf8@kuoka>
Date: Fri, 20 Jun 2025 09:22:04 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Hardik Garg <hargar@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org, 
	decui@...rosoft.com, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	devicetree@...r.kernel.org, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ssengar@...ux.microsoft.com, hargar@...rosoft.com, apais@...rosoft.com
Subject: Re: [PATCH v4 2/2] vmbus: retrieve connection-id from DeviceTree

On Thu, Jun 19, 2025 at 04:06:35PM GMT, 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@...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)

Your binding said connection ID 0 is a valid one, so this is wrong. Or
binding is wrong.

Best regards,
Krzysztof