linux-kernel - Re: linux-next: Tree for Apr 20 (usb & target)

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Date:	Thu, 03 May 2012 20:34:23 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-usb@...r.kernel.org, target-devel@...r.kernel.org,
	Felipe Balbi <balbi@...com>
Subject: Re: linux-next: Tree for Apr 20 (usb & target)

On Sun, 2012-04-22 at 21:01 +0200, Sebastian Andrzej Siewior wrote:
> * Greg KH | 2012-04-21 08:34:02 [-0700]:
> 
> >> > CONFIG_MODULES is not enabled.
> >> > CONFIG_TCM_USB_GADGET=y
> >> > CONFIG_USB_GADGET=y
> >> 
> >> Sebastian + Greg-KH (Cc'ed), any ideas why this is the case here..?
> >
> >I have no idea, sorry.
> 
> The short version:
> in order to fix this either move the usb-target-gadget to
> drivers/usb/gadget/Kconfig and make sure only one gadget can be compiled
> at a time or add some kind of depends.
> 
> The longer version:
> This is a short comming of the gadget framework. We are able to build
> multiple UDCs at a time and we can build multiple gadgets _as_ modules.
> Since we can not bind & configure via an interface the whole thing works
> right now via "modprobe $gadget. There is some infrastructure to accept
> multiple UDCs/gadget but the *whole* thing is not complete.
> In non-modules mode you can only select one gadget at a time. With the
> target gadget living outside of usb/gadget selection it is possible to
> select both at the same time which causes the duplicate symbols here.
> A "quick" fix is not to define all the functions static and put
> maybe_unsued on each function to avoid warnings. This is only duct tape
> on top and I would prefer that nobody is sending such a patch. The
> result is hardly usefull by a user.
> A real fix would to get rid of the "#includes foo.c" and use a helper
> module/library instead.
> I tried this once and notice that the whole thing relies on
> static/global variables which are initialized once on modprobe. So
> with the second module loaded (read as rmmod $mod1 && modprobe $mod2)
> the gadget framework explodes. Once I noticed that, the patches got out
> of Felipe's tree before anyone noticed something. That means we should
> first get rid of the global variables and then maybe try again :)
> 

Hey Sebastian & USB folks,

So I'm catching up on for-next-merge stuff after being away last week,
and ended up following your advice to just move tcm_usb_gadget code into
drivers/usb/gadget/ in to address the legacy requirements above..

After the recommended change, the in-kernel config using a single gadget
driver (the target) are able to build.  Thanks for the detailed
explanation btw.. ;)

I've made the same change for tcm_usb_gadget in lio-core, and updated
for-next-merge with the following merge patch:

http://git.kernel.org/?p=linux/kernel/git/nab/target-pending.git;a=commit;h=0c41520201bc0933d65b8644173802778f426234

Please let me know if you have any other changes that should go into
sunday's linux-next build.

Thanks!

--nab

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