Re: Complex I2C device

[Rodolfo Giometti <giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org>]

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On Wed, Jan 30, 2008 at 09:32:38PM +0100, Guennadi Liakhovetski wrote:
> Hi Rodolfo,
> 
> On Wed, 30 Jan 2008, Rodolfo Giometti wrote:
> 
> > my custom board has a «complex» device... let me explain better: it's
> > formed by a custom I2C device and an I/O extender PCA9539.
> > 
> > Ascii art:
> > 
> > 
> >                 +---------+
> >           --+---+         |
> >             |   | PCA9539 |
> >             |   +---------+
> > Bus I2C ->> |      | | |
> >             |      | | | <<--- GPIOs
> >             |      | | |
> >             |   +---------+
> >             +---+         |
> >                 |   CHIP  |
> >                 +---------+  
> > 
> > Some input GPIOs of CHIP are managed by the PCA9539. So fisically I
> > have two devices but logically they are merged together into one.
> > 
> > I can send commands to CHIP by both I2C bus and the GPIOs, which in
> > turn are controlled by the PCA9539.
> > 
> > Can you please suggest me the best way to manage this problem? My
> > solution was to provide PCA9539's driver of some exported symbols and
> > using them into the CHIP's driver. Is that right? Or, can I "call" (in
> > any way) PCA9539 driver's methods from CHIP's driver?
> 
> First, you want to use gpiolib, which in -mm tree now lives under 
> drivers/gpio and includes a driver for pca9539. With it the pca9539 driver 
> registers a gpio controller with the system, and then your driver for the 
> other part can just request respective GPIOs as if they were normal CPU 
> GPIOs or whatever else. And toggle them using the standard API. I will 
> (hopefully tomorrow) post an example of exactly this to the 
> video4linux-list-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org list. In my case this other chip is a CMOS 
> camera.

Great, this would be a good solution for this scenario... but I'm
looking something more "general". A related problem of mine is on
another custom board which has the following:


                 +---------+
           --+---+ Battery |
             |   | Manager |
             |   +---------+
 Bus I2C ->> |
             |
             |
             |   +---------+
             +---+         |
                 |  CHIP   |
                 +---------+

A (complex) battery pack are managed by a "battery manager" and a
custom chip connected by the I2C bus (my hardware designer _loves_ I2C
bus :). Even these devices can be logically considered as only one
(big) battery...

Looking at I2C code, which uses the new style driver model, I see the
function i2c_register_board_info() where we can specify the bus number
and the devices list attached on that I2C bus, so I suppose we can add
a function as:

	struct i2c_client *i2c_find_client(int busnum, unsigned short addr);

which can return the i2c_client struct associated to the given bus
number and i2c address.

This should resolve any possible problem related to every I2C
"complex" device. Shouldn't it?

Thanks for your help,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org
Linux Device Driver                             giometti-kaDoWcXyVrEAvxtiuMwx3w@public.gmane.org
Embedded Systems                     		giometti-k2GhghHVRtY@public.gmane.org
UNIX programming                     phone:     +39 349 2432127

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