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

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Message-ID: <CACVXFVN=i10cVS3RQ7jGrJAfsC+r2t61z7XOVKWMAMqKKELZCg@mail.gmail.com>
Date:	Wed, 6 Mar 2013 11:03:40 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Bjørn Mork <bjorn@...k.no>
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

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:
>> Ming Lei <ming.lei@...onical.com> writes:
>>
>> I am starting to wonder why the USB core has combined system suspend and
>> runtime suspend if we are going to end up with every driver testing
>> PMSG_IS_AUTO(message) and selecting a completely different code path.
>>
>> You are right that we will end up with problems if usbnet_resume is
>> called for a device usbnet hasn't suspended.  But I'd still claim that
>> is a bug in the USB core, which is the one that decided to ignore the
>> suspend error and still call resume.
>>
>> 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.

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

Thanks,
--
Ming Lei
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