linux-kernel - Re: [PATCHv4 2.6.25] i2c: adds support for i2c bus on Freescale CPM1/CPM2 controllers

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Message-ID: <47C18A4E.5080804@scram.de>
Date:	Sun, 24 Feb 2008 16:16:30 +0100
From:	Jochen Friedrich <jochen@...am.de>
To:	Olof Johansson <olof@...om.net>
CC:	Jean Delvare <khali@...ux-fr.org>, linux-kernel@...r.kernel.org,
	linuxppc-dev list <linuxppc-dev@...abs.org>,
	i2c@...sensors.org, Scott Wood <scottwood@...escale.com>
Subject: Re: [PATCHv4 2.6.25] i2c: adds support for i2c bus on Freescale	CPM1/CPM2
 controllers

Hi Olof,

>> 2. record the I2c name in the dts tree, either as seperate tag (like linux,i2c-name="<i2c-name>")
>>    or as additional compatible entry (like compatible="...", "linux,<i2c-name>").
> 
> I have to say no on this one. The device tree is not supposed to know
> about how linux uses devices, there are firmwares out there that don't
> use DTS for thier device trees, etc.

I still believe this this could be done for embedded devices which are usually booted
via wrapper or U-Boot as those devices will most probably use the most exotic I2c devices
out there (e.g. home-grown devices used by stbs). However, I'm not an device tree expert.
 
>> 3. use a glue layer with a translation map.
> 
> In my opinion this is an OK solution since the same information has to
> be added somewhere already anyway -- eiither to the drivers or to this
> translation table. It should of course be an abstacted shared table,
> preferrably contained under the i2c source directories since several
> platforms and architectures might share them.

I could think of a mixture between 2. and 3.:

Using the compatible attribute with the manufacturer stripped off as I2c name by default
and using an exception table. For now, the struct i2c_driver_device would currently only
need one entry ("dallas,ds1374", "rtc-ds1374").

Thanks,
Jochen
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