linux-kernel - RE: [PATCH] Drivers: hv: vmbus: Don't wait for the ACPI device upon initialization

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Date:   Thu, 22 Sep 2022 21:59:19 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
        Stanislav Kinsburskii <skinsburskii@...rosoft.com>
CC:     Stanislav Kinsburskiy <stanislav.kinsburskiy@...il.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] Drivers: hv: vmbus: Don't wait for the ACPI device upon
 initialization

From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com> Sent: Wednesday, September 21, 2022 11:39 AM
> 
> Waiting to 5 seconds in case of missing VMBUS ACPI device is redundant as the

A nit:  We've been all over the map on the capitalization of "VMBus".  Somebody
outside of Microsoft recently did a census in the Linux code and commits, and
"VMbus" is the most popular, closely followed by "VMBus".  The preferred approach
in Microsoft public documentation is "VMBus", so that's what we should try to 
use going forward.  Not "VMBUS" and not "vmbus", though the latter is fine in
variable and function names.

> device is either present already or won't be available at all.
> This patch enforces synchronous probing to make sure the bus traversal,
> happening upon driver registering will either find the device (if present) or
> not spend any additional time if device is absent.
> 
> Signed-off-by: Stanislav Kinsburskiy <stanislav.kinsburskiy@...il.com>
> CC: "K. Y. Srinivasan" <kys@...rosoft.com>
> CC: Haiyang Zhang <haiyangz@...rosoft.com>
> CC: Stephen Hemminger <sthemmin@...rosoft.com>
> CC: Wei Liu <wei.liu@...nel.org>
> CC: Dexuan Cui <decui@...rosoft.com>
> CC: linux-hyperv@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> ---
>  drivers/hv/vmbus_drv.c |   13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 7b9f3fc3adf7..32d0009631a6 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -46,8 +46,6 @@ struct vmbus_dynid {
> 
>  static struct acpi_device  *hv_acpi_dev;
> 
> -static struct completion probe_event;
> -
>  static int hyperv_cpuhp_online;
> 
>  static void *hv_panic_page;
> @@ -2468,7 +2466,6 @@ static int vmbus_acpi_add(struct acpi_device *device)
>  	ret_val = 0;
> 
>  acpi_walk_err:
> -	complete(&probe_event);
>  	if (ret_val)
>  		vmbus_acpi_remove(device);
>  	return ret_val;
> @@ -2647,6 +2644,7 @@ static struct acpi_driver vmbus_acpi_driver = {
>  		.remove = vmbus_acpi_remove,
>  	},
>  	.drv.pm = &vmbus_bus_pm,
> +	.drv.probe_type = PROBE_FORCE_SYNCHRONOUS,
>  };
> 
>  static void hv_kexec_handler(void)
> @@ -2719,7 +2717,7 @@ static struct syscore_ops hv_synic_syscore_ops = {
> 
>  static int __init hv_acpi_init(void)
>  {
> -	int ret, t;
> +	int ret;
> 
>  	if (!hv_is_hyperv_initialized())
>  		return -ENODEV;
> @@ -2727,8 +2725,6 @@ static int __init hv_acpi_init(void)
>  	if (hv_root_partition)
>  		return 0;
> 
> -	init_completion(&probe_event);
> -
>  	/*
>  	 * Get ACPI resources first.
>  	 */
> @@ -2737,9 +2733,8 @@ static int __init hv_acpi_init(void)
>  	if (ret)
>  		return ret;
> 
> -	t = wait_for_completion_timeout(&probe_event, 5*HZ);
> -	if (t == 0) {
> -		ret = -ETIMEDOUT;
> +	if (!hv_acpi_dev) {
> +		ret = -ENODEV;
>  		goto cleanup;
>  	}
> 
> 

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>