linux-kernel - Re: Frame buffers and early i2c

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Date:	Mon, 9 Jun 2008 23:59:35 +0200
From:	Uli Luckas <u.luckas@...d.de>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	linux-kernel@...r.kernel.org, adaplas@...il.com,
	Linux I2C <i2c@...sensors.org>
Subject: Re: Frame buffers and early i2c

On Monday 09 June 2008, Jean Delvare wrote:
> On Mon, 9 Jun 2008 16:47:42 +0200, Uli Luckas wrote:
> > I am in the process of trying out a display connected to a colibri
> > board's pxa frame buffer device. The display's power supply is switch
> > through i2c.
> >
> > In order to use the frame buffer console I have i2c and pxafb compiled
> > in.
> >
> > By default, the pxafb driver get's initialized before the i2c bus causing
> > the display power up to fail.
> >
> > What do i2c people think about changing the link order here?
>
> Why don't you ask on the i2c mailing list? Cc added.
>
I wanted to get i2c developers plus frame buffer and other i2c client 
developers involved. Crossposting to more then 2 lists seemed wrong.

> Personally I have no objection, but dependencies can be tricky so
> you'll have to be careful. video is early in the link order at the
> moment.
>
Yep. I might come back for help on that later.

> > What do other frame buffer drivers handle the absence of i2c during early
> > boot?
>
> Interestingly enough, they appear to do fine, despite the linking
> order. Maybe because i2c_init is a subsys_initcall() while framebuffer
> drivers are initialized with module_init()? Then I'm not sure why your
> own driver has a problem there.
>
Well, this is only very partially true. Try:
rgrep -l subsys_initcall drivers/i2c/
rgrep -l module_init drivers/i2c/

The last of which gives drivers/i2c/busses/i2c-pxa.c for example.

I'll change the pxa i2c driver to subsys_initcall and try if that works when I 
get back to my desk tomorrow.

regards,
Uli
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