linux-kernel - Re: [PATCH] usb: avoid PM error messages during resume if a device was disconnected

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Date:	Mon, 23 Mar 2009 17:44:31 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Frans Pop <elendil@...net.nl>
cc:	linux-usb@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	<linux-pm@...ts.linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: avoid PM error messages during resume if a device
 was disconnected

On Mon, 23 Mar 2009, Frans Pop wrote:

> Currently if a laptop is suspended e.g. while docked and then resumed after
> undocking it, the following errors get generated because the USB hub in the
> docking station and the devices connected to it are no longer available:
> pm_op(): usb_dev_resume+0x0/0x10 returns -19
> PM: Device 1-2 failed to resume: error -19
> pm_op(): usb_dev_resume+0x0/0x10 returns -19
> PM: Device 1-2.2 failed to resume: error -19
> pm_op(): usb_dev_resume+0x0/0x10 returns -19
> PM: Device 1-2.3 failed to resume: error -19
> 
> As the removal of USB devices while a system is suspended is a relatively
> common use case and in most cases not an error, just return success on
> -ENODEV. The user gets informed anyway as the USB subsystem generates
> regular disconnect messages for the devices shortly afterwards:
> usb 1-2: USB disconnect, address 3
> usb 1-2.2: USB disconnect, address 4
> usblp0: removed
> usb 1-2.3: USB disconnect, address 5
> 
> Signed-off-by: Frans Pop <elendil@...net.nl>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> ---
> 
> I've walked through the code and AFAICT just returning 0 does not make any
> difference for the PM core code.

That's right.  After all, there isn't much the PM core can do when an 
error occurs.

> In a first version of this patch I had the following included just before
> the 'return 0':
> 	pr_info("usb %s: failed to resume: no longer connected\n",
> 						dev_name(&udev->dev));
> 
> Problem with that was that the message got printed twice for each device,
> once for .resume and once for .complete. Given that the disconnects are
> reported shortly after anyway, I decided the simpler patch might do just
> as well.
> 
> Cheers,
> FJP
> 
> diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
> index d0a21a5..97ea69b 100644
> --- a/drivers/usb/core/driver.c
> +++ b/drivers/usb/core/driver.c
> @@ -1727,6 +1727,10 @@ int usb_external_resume_device(struct usb_device *udev, pm_message_t msg)
>  	status = usb_resume_both(udev, msg);
>  	udev->last_busy = jiffies;
>  	usb_pm_unlock(udev);
> +
> +	if (status == -ENODEV)
> +		return 0;
> +
>  	if (status == 0)
>  		do_unbind_rebind(udev, DO_REBIND);

Please include a short comment explaining the reason for this test 
(i.e., that there's no advantage in producing an error message since 
the regular disconnect messages will be generated shortly).

Or do you think maybe it would be better to move this test up into the
PM core?  After all, other subsystems will face the same issue.  I 
think that would be the best approach.  Yes?

Alan STern

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