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

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Message-ID: <87fw09nd2a.fsf@nemi.mork.no>
Date:	Wed, 06 Mar 2013 09:32:29 +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:

> Here is one link I found:
>
>        http://marc.info/?l=linux-usb&m=132557022902261&w=2

Thanks.  This section caught my eye:

    "The USB suspend/resume code is full of those crazy "let's use one
     function, and pass it as an *argument* what to do". It's a disease.
     The PM layer used to do the same thing (PMSG_xyz crap), and we've
     largely gotten rid of it, but USB still plays around with those things
     and makes it even *worse* exactly with these kinds of
     "do_unbind_rebind()" routines that then look at the argument instead
     of having a sane routine for unbinding and another sane routine for
     re-binding."


I take that as supporting my view on all the "if (PMSG_IS_AUTO(msg)"
testing...

But I don't have any ideas on how to fix it now that you all have spoon
fed me the background.

> IMO, we unbind interface which hasn't suspend/resume callback
> during suspend because there is no better way to handle the case.
> But for the suspend failure case, maybe rebind isn't necessary, and
> we can document that drivers have to handle their system suspend
> failure in resume(), where it is very suitable to do PM recovery.

Yup, agreed, although I fear that if Alan's commit messages are confused
then I unable explain anything like this ;)

> Also we may store the failure code into usb_interface, and let
> USB core check if the suspend failure has been handled/cleared
> after resume().

That sounds unnecessarily complicated.  Let the driver deal with
it, keeping the API as simple as possible.


Bjørn
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