netdev - Re: [PATCHv4] usbnet: Resubmit interrupt URB once if halted

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Message-ID: <BANLkTikjRzBjQ7uar+GDSGsPvK8snY84rQ@mail.gmail.com>
Date:	Fri, 22 Apr 2011 07:59:18 -0700
From:	Paul Stewart <pstew@...omium.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	netdev@...r.kernel.org, USB list <linux-usb@...r.kernel.org>
Subject: Re: [PATCHv4] usbnet: Resubmit interrupt URB once if halted

On Thu, Apr 21, 2011 at 11:48 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Thu, 21 Apr 2011, Paul Stewart wrote:
>
>> > The driver needs better coordination between open/stop and
>> > resume/suspend. �The interrupt and receive URBs are supposed to be
>> > active whenever the interface is up and not suspended, right? �Which
>> > means that usbnet_resume() shouldn't submit anything if the interface
>> > isn't up.
>>
>> How do we define "up" here (from a network perspective there are many
>> ways to interpret that)?  How does this concept compare to the user's
>> "ifconfig up/down" state?
>
> I don't know the details of how network drivers are supposed to work.
> But it doesn't matter -- for your purposes you should define "up" to
> mean "whenever the URBs are supposed to be active (unless the interface
> is suspended)".
>
>>  What call do I use in usbnet_resume() to
>> tell that the interface isn't up?  Currently I'm using netif_running()
>> which responds true in this condition, which is why I'm resorting to
>> the flag.
>
> Again, I don't know.  However, the URBs get submitted from within
> usbnet_open() and killed within usbnet_stop(), right?  Therefore you
> can use any condition which gets set to True in usbnet_open() and set
> to False in usbnet_stop().  (If nothing else is suitable, use a flag of
> your own.)

This is exactly the situation I'm in.  I couldn't find any other
driver or network state that cleanly represented the stop/start state
of the driver.  I'll post a new patch that uses an OPEN flag instead
of an interrupt halted flag, a GFP_NOIO flag, and kills and frees the
interrupt URB on usb_disconnect().

>  And be careful of the edge case: Since usbnet_open() itself
> performs a resume operation, you need to make sure the resume takes
> place before the condition becomes True -- otherwise the URBs will get
> submitted twice.
>
> One more thing to keep in mind: If the kernel is built without PM
> support, the resume and suspend routines will never get called.
> Therefore they must not be the only places where URBs are submitted and
> killed.
>
> Alan Stern
>
>
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