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

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Message-ID: <BANLkTikK66s2fWY7LToRmgH_iGfhkFV01A@mail.gmail.com>
Date:	Thu, 21 Apr 2011 07:44:04 -0700
From:	Paul Stewart <pstew@...omium.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	davem@...emloft.net, greg@...ah.com
Subject: Re: [PATCHv4] usbnet: Resubmit interrupt URB once if halted

On Thu, Apr 21, 2011 at 6:43 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Wed, 20 Apr 2011, Paul Stewart wrote:
>
>> On Wed, Apr 20, 2011 at 2:08 PM, Alan Stern <stern@...land.harvard.edu> wrote:
>> > On Tue, 19 Apr 2011, Paul Stewart wrote:
>> >
>> >> Set a flag if the interrupt URB completes with ENOENT as this
>> >> occurs legitimately during system suspend. �When the usbnet_bh
>> >> is called after resume, test this flag and try once to resubmit
>> >> the interrupt URB.
>> >
>> > No doubt there's a good reason for doing things this way, but it isn't
>> > clear. �Why wait until usbnet_bh() is called after resume? �Why not
>> > resubmit the interrupt URB _during_ usbnet_resume()?
>>
>> Actually, I was doing this in the bh because of feedback I had gained
>> early in this process about not doing submit_urb in the resume().
>
> Do you have a URL for that feedback?  In general, there's no reason not
> to resubmit URBs during a resume callback; lots of drivers do it.  But
> usbnet may have some special requirements of its own that I'm not aware
> of.
>
>>  If
>> that issue doesn't exist, that makes my work a lot easier.  In testing
>> I found that just setting this to happen in the bh might be problematic
>> due to firing too early, so this is good news.
>>
>> >�This would seem
>> > to be the logical approach, seeing as how usbnet_suspend() kills the
>> > interrupt URB.
>>
>> Aha!  But you'll see from the current version of my patch that we don't
>> actually ever kill the interrupt URB.  It gets killed all on its own (by the
>> hcd?) and handed back to us in intr_complete().  This last bit about the
>> complete function being called was lost on me for a while which is why
>> in a previous iteration of the patch I was trying to kill the urb in suspend().
>
> Why not kill the interrupt URB while suspending?  It's the proper thing
> to do.  Otherwise you run the risk that an event might happen at just
> the wrong time, causing the interrupt URB to complete normally, but
> _after_ the driver has finished suspending.  There's a good chance the
> driver would not process the event correctly.

I don't mind killing the URB. I'd want to set the halt flag as well
(more on why have a flag in response to your other email).  You're
right that there may be a race between an interrupt URB arriving and
the onset of suspend, but I really can't imagine why I can't solve
that by setting the flag if a submit_urb() fails in intr_complete().

>
> Alan Stern
>
>
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