netdev - Re: [PATCH 1/2] usbnet: allow status interrupt URB to always be active

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Message-ID: <1357572310.27649.10.camel@dcbw.foobar.com>
Date:	Mon, 07 Jan 2013 09:25:10 -0600
From:	Dan Williams <dcbw@...hat.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Elina Pasheva <epasheva@...rrawireless.com>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Rory Filer <rfiler@...rrawireless.com>,
	Phil Sutter <phil@....cc>
Subject: Re: [PATCH 1/2] usbnet: allow status interrupt URB to always be
 active

On Sat, 2013-01-05 at 12:01 +0100, Oliver Neukum wrote:
> On Friday 04 January 2013 19:26:33 Dan Williams wrote:
> > On Fri, 2013-01-04 at 23:16 +0100, Oliver Neukum wrote:
> > > On Friday 04 January 2013 10:48:16 Dan Williams wrote:
> > > > Some drivers (ex sierra_net) need the status interrupt URB
> > > > active even when the device is closed, because they receive
> > > > custom indications from firmware.  Allow sub-drivers to set
> > > > a flag that submits the status interrupt URB on probe and
> > > > keeps the URB alive over device open/close.  The URB is still
> > > > killed/re-submitted for suspend/resume, as before.
> > > > 
> > > > Signed-off-by: Dan Williams <dcbw@...hat.com>
> > > > ---
> > > > Oliver: alternatively, is there a problem with *always*
> > > > submitting the interrupt URB, and then simply not calling
> > > > the subdriver's .status function when the netdev is
> > > > closed?  That would be a much simpler patch.
> > > 
> > > That is quite radical. We have no idea what a device
> > > does when we do not react to a status update. I would
> > > much prefer to not take the risk.
> > > Besides, we don't use bandwidth if we don't have to.
> > 
> > Ok, so scratch the alternative.  Thus, does the posted patch look like
> > the right course of action?
> 
> In principle yes.
> 
> > If I wasn't clear enough before, sierra_net needs to listen to the
> > status interrupt URB to receive the custom Restart indication as part of
> > the driver's device setup.  Thus for sierra_net at least, tying the
> > status interrupt URB submission to device open/close isn't right.
> 
> So, there seems to be an inevitable race before probe() is called.

Yeah, you're right, we need Sierra to send the SYNC message *after* bind
is called.    Is there an existing "after bind" hook or do we need to
create one?

> Have you looked at FLAG_AVOID_UNLINK_URBS ?

Not yet, but I will.

Thanks,
Dan

> > I'd previously done a patch to handle this all in sierra_net, but the
> > problem there is suspend/resume: without directly accessing the usbnet
> > structure's ->suspend_count member (icky!) sierra_net can't correctly
> > kill/submit the URB itself.  So I went with a flag to usbnet that Sierra
> > can set.
> 
> That is absolutely the right way to do it.
> 
> 	Regards
> 		Oliver
> 
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