linux-kernel - Re: [PATCH] USB: gadget driver for LPC32xx

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Message-ID: <4F68CA5C.2090406@antcom.de>
Date:	Tue, 20 Mar 2012 19:20:12 +0100
From:	Roland Stigge <stigge@...com.de>
To:	Arnd Bergmann <arnd@...db.de>
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	w.sang@...gutronix.de, kevin.wells@....com,
	linux-arm-kernel@...ts.infradead.org, arm@...nel.org,
	srinivas.bakki@....com
Subject: Re: [PATCH] USB: gadget driver for LPC32xx

Hi Arnd,

On 03/20/2012 02:01 PM, Arnd Bergmann wrote:
>> Maybe the right thing is a common low-level isp1301 interface defining
>> all the registers and providing low-level (I2C) access functions,
>> leaving all the "higher level"/"board specific" functions up to the
>> existing drivers?
>>
>> (I guess you meant drivers/usb/otg/isp1301_omap.c ?)
> 
> Yes, that sounds like a very good idea. Can you describe which part of
> the function isp1301 does? It's not clear how the layering between
> that and the platform driver should end up.

The ISP1301 is a relatively simple transceiver where the actual
differential USB signals end up being generated/decoded. It contains
some registers and is controlled via I2C to manipulate electrical
settings (pull up / power etc.).

At a first glance, I found the following drivers to be using it:

ohci-nxp (was: ohci-pnx4008 + ohci-lpc32xx)
isp1301_omap
lpc32xx_udc (WIP)

The common functions that all of them are using are some low-level
functions like read/write byte, read/write word. (For ohci-nxp, I used
smbus commands.) I propose exporting just the defines for all the
registers and their bits together with some accessor functions.

Would those be the correct places for header and driver:

drivers/usb/misc/isp1301.c
include/linux/usb/isp1301.h

?

As an example usage, I would let the next update of the lpc32xx_udc use
it and separately provide patches to make the other drivers above also
use it.

Thanks in advance,

Roland
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