linux-kernel - Re: [PATCH] Allow MUSB DSPS to use "force host" mode

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Message-ID: <528F8B35.8070408@newflow.co.uk>
Date:	Fri, 22 Nov 2013 16:49:57 +0000
From:	Mark Jackson <mpfj-list@...flow.co.uk>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	linux-usb@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Greg KH <gregkh@...uxfoundation.org>, jkosina@...e.cz,
	anatol.pomozov@...il.com,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Bin Liu <binmlist@...il.com>
Subject: Re: [PATCH] Allow MUSB DSPS to use "force host" mode

On 22/11/13 16:33, Sebastian Andrzej Siewior wrote:
> On 11/22/2013 04:55 PM, Mark Jackson wrote:
>> The IDDIG input pin is normally used to determine the USB mode
>> (i.e. HOST or DEVICE).
>>
>> On some systems (e.g. AM335x) leaving this pin floating allows
>> the USB mode to be set via software.
> 
> So you have a board where musb is used only as host or only as device
> and the ID pin not on ground or 3.3V?
> What are the side effects? I remember correctly Bin wanted to avoid
> settings this if it could be avoided.

Yes ... we have a host only USB port and an unconnected ID pin.

AFAIK it defaults to device mode so I can't see any devices that get
plugged into the USB port.

If I tweak the s/w to "force" host mode on, then everything appears to
work okay.

I guess it's more of a hardware oversight that we left the pin floating
but in the real world, I guess someone may want this feature to they
can change the usb port type ?

Either way, I need to fix the current h/w (which can be done via s/w)
hence the patch.

Mark J.

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