linux-kernel - Enabling multiple gadgets on top of composite driver

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Message-ID: <D5ECB3C7A6F99444980976A8C6D896384FA30FA942@EAPEX1MAIL1.st.com>
Date:	Fri, 13 Apr 2012 18:51:26 +0800
From:	Bhupesh SHARMA <bhupesh.sharma@...com>
To:	"balbi@...com" <balbi@...com>
Cc:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>
Subject: Enabling multiple gadgets on top of composite driver

Hi,

I have a query regarding enabling multiple gadgets (like g_webcam, g_zero etc..)
on top of the Composite driver.

My use case is very simple:
	- I want to expose a USB composite device to a standard USB host, where
	  the Composite device supports a webcam gadget + zero gadget + some other gadget..

On the older kernels like 2.6.27, this was easily possible, but the latest
gadget code doesn't seem to support the same:
	- I can see that first a 'choicemenu' is provided which allows selection of only
	  one gadget at a time.

	- The "common" stuff like "composite.c", "epautoconfig.c" have been included in
	  each f_* function driver (for e.g. f_uvc.c, f_sourcesink.c, etc..), so even if
	  I somehow tweak the 'choicemenu' stuff, I get redeclaration errors.

	- If I somehow separate the "common" stuff and compile the same separately and
	  then compile zero gadget, webcam gadget etc.., I see that the 'usb_composite_probe'
	  call of only the 1st gadget passes correctly, but from the 2nd gadget driver
        onwards as 'composite' is already present the following check in 'usb_composite_probe'
	  fails:

		if(!driver || !driver->dev || !bind || composite)
			return -EINVAL;

I am hoping someone else must also have faced an issue like this before..

What is the best way to enable multiple gadgets (like g_webcam, g_zero etc..)
on top of the Composite driver or am I missing something here?

Regards,
Bhupesh
	
 
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