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SubjectRe: i2c tuner initialization
On Mon, 5 Apr 1999, Michel LESPINASSE wrote:

>
> Hello,
>
> I am currently looking at the way the tuner is initialized in the bttv
> driver (from pristine 2.2.5 kernel sources) and I'm getting confused.
>
> Basically, it all started when I wondered if I could get the tuner module
> to be autoloaded by kmod (and I still dont manage to do this)

post-install bttv modprobe -k tuner

> My understanding is that the interface with the i2c bus module goes like
> this :

[ ... ]

> * It may introduce address clashes that could be avoided with a better
> interface. Suppose I have two different i2c busses in my computer.

A driver can allways check the bus id.

> * the bus owner explicitly probes for the types of devices that he expects
> to find on its i2c bus. For example, the bttv bus owner would probe for
> tuner and msp3400 devices, because this is what he expects and he wouldnt
> know how to use other devices if they were present anyway. This probing
> would go like this : instead of waiting for the callback attach_inform
> (bus, driver_id) to be called, the bus owner would directly call a
> function i2c_probe_device (bus, driver_id) and this function would return
> a boolean indicating if a device of this type was found on this bus.

You can have modules which are independent from the device which is the
i2c bus master. For example video text chips, a character device for i2c
access, ...)

> Do you think I should work on this ? Is there some advantages to the
> current system that I do not see ?

It has one major design flaw: It can handle only simple bit-controllers.
More clever i2c controllers (which can do complete bus-cycles in hardware
for example) can't be handled.

See also: http://www.tk.uni-linz.ac.at/~simon/private/i2c/v4l/

Gerd



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