linux-kernel - Re: Odd behavior in musb_hdrc OTG if gadget drivers are modules

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Message-ID: <20090225211716.GD4639@gandalf>
Date:	Wed, 25 Feb 2009 23:17:17 +0200
From:	Felipe Balbi <me@...ipebalbi.com>
To:	david.hagood@...il.com
Cc:	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Odd behavior in musb_hdrc OTG if gadget drivers are modules

On Thu, Jan 22, 2009 at 03:46:28PM -0600, david.hagood@...il.com wrote:
> I've spend the day tracking down a weird behavior on a Beagleboard with
> 2.6.29-rc2-omap1.
> 
> If you select the mode for the musb to operate in OnTheGo mode
> (CONFIG_USB_MUSB_OTG), and if you compile the gadget drivers as modules,
> the the USB port will NOT be brought up at system boot, even if it has a
> USB mini-A cable plugged in (and thus should be in host mode, not gadget
> mode).
> 
> If you then modprobe an appropriate gadget driver, then the interface will
> be brought up in host mode.

that's expected. When you have otg selected, you can only let musb work
when it's fully functional on both roles ;-)

> If you DON'T modprobe a gadget driver, AND you attempt to force the port
> to host mode by
>   echo host > /sys/devices/platform/musb_hdrc/mode
> 
> Then we get a kernel page fault trying to change modes, even though we are
> changing to host mode, which should be valid.
> 
> It seems to me that either the port should be brought up in host mode if
> no gadget drivers are loaded, and an attempt to switch to gadget mode
> should fail if no driver is loaded, OR there should be a config options to
> set what the default gadget driver is in the absence of one being loaded
> by the system.

not really, imagine what would happen, for example, if when you don't
have a gadget driver loaded, the other side tries HNP...

-- 
balbi
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