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

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Message-ID: <20120413105921.GM7154@arwen.pp.htv.fi>
Date:	Fri, 13 Apr 2012 13:59:23 +0300
From:	Felipe Balbi <balbi@...com>
To:	Bhupesh SHARMA <bhupesh.sharma@...com>
Cc:	"balbi@...com" <balbi@...com>,
	"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: Re: Enabling multiple gadgets on top of composite driver

On Fri, Apr 13, 2012 at 06:51:26PM +0800, Bhupesh SHARMA wrote:
> 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..

look at how nokia.c does it.

> 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.

Answer M instead of Y to "USB Gadget Drivers"

> 	- 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.

yeah, that still needs to be cleaned up. The story behind that is very
long.

> 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?

Either you want multiple gadgets or you want a composite gadget, what is
it ? If you want a composite gadget, you need to write a small C file
which combines multiple functions together (see nokia.c), if you want
multiple gadget drivers, just make them all modules. I always compile
all gadget drivers as modules and can use any one of them at any time.

-- 
balbi

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