netdev - Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

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Date:	Wed, 06 Mar 2013 08:06:10 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

Ming Lei <ming.lei@...onical.com> writes:
> On Wed, Mar 6, 2013 at 10:51 AM, Ming Lei <ming.lei@...onical.com> wrote:
>> On Wed, Mar 6, 2013 at 12:08 AM, Bjørn Mork <bjorn@...k.no> wrote:
>>
>>> I guess proper error handling here require the USB core to see the
>>> interface driver as dead if it fails to suspend on system suspend, and
>>> do forced rebinding on resume.
>>
>> The idea should be fine, but may cause regression of user space, suppose
>> one device with suspend failure can be across suspend-resume cycle and
>> work well before, but it is no longer with your forced rebinding.
>
> Give the potential cost(user space regression) of doing rebind, I think it
> is better to try to recover the device in resume() first, then
> consider rebinding
> as the last straw.  In fact, I am also wondering if resume() can't recover one
> device but probe() can, maybe we can always let resume() recover the
> device which experienced suspend failure.

Yes, sure. Drivers wanting to do this, anticipating typical errors, can
still return 0 from suspend and do whatever they want in resume.

My proposal is to make the USB core properly deal with drivers returning
an error from suspend, and also document the fact that a driver should
always return 0 on system suspend unless it really want forced unbinding
on suspend errors.

> I remember that some guys went against rebinding during system sleep before
> in the firmware loading discussion.

Yes, that is probably relevant. I'll look it up.  Thanks for the
pointer.


Bjørn
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