linux-kernel - Re: [PATCH 4/7] gpiolib: implement dev_gpiochip

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Date:	Thu, 23 Oct 2008 02:29:40 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Brownell <david-b@...bell.net>
Cc:	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, i2c@...sensors.org,
	Jean Delvare <khali@...ux-fr.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH 4/7] gpiolib: implement dev_gpiochip_{add,remove} calls

On Wed, Oct 22, 2008 at 02:52:46PM -0700, David Brownell wrote:
> On Wednesday 22 October 2008, Anton Vorontsov wrote:
> > > 
> > > > So if we register the board infos after 
> > > > the controller registered, then nobody will probe the board infos.
> > > 
> > > See above.  If you're doing it right, there's no problem.
> > > That is, scan the OF tables early.  Just like PNP tables
> > > get scanned early, for example.
> > 
> > Heh. If we don't want to be able to make the OF-parsing code
> > be a module then there is no problem at all. I can use the bus
> > notifiers. And it is most straightforward solution then.
> > 
> > But I quite dislike to bloat the kernel image with
> > maybe-never-used-on-this-board code.
> 
> So have it live in the __init text section.  If you're
> building a kernel with support for several boards, you
> know it's necessarily going to be larger than it would
> be if only one board were supported.  But you can shrink
> kernel size by judicious use of __init sections..

Won't work, unfortunately. I2C devices are created by the
i2c controllers, via drivers/of_i2c.c  of_register_i2c_devices().

There is a good reason to do so, the code needs to know
controller's OF node to walk down and register the child nodes
(devices). See drivers/i2c/busses/i2c-mpc.c -- it calls
of_register_i2c_devices() at the end of the probe().

Since we can't call __init stuff from non-__init, the scheme
you purpose won't work.

The same is for SPI (drivers/of_spi.c of_register_spi_devices()).

> > My aim was to make the 
> > OF-parsing part be a module too. Because in the long run we
> > need the OF-parsing stuff for _every_ driver that needs
> > platform data. It's quite expensive to have it always built-in,
> > don't you think?
> 
> If it's discarded early, after translating the data from
> OF format into what the drivers need, there will be no
> RAM footprint.

There is also kernel image size that matters...

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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