linux-kernel - Re: qestion about I2C_CLASS

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Date:	Fri, 5 Sep 2008 10:57:56 +0200
From:	"Francis Moreau" <francis.moro@...il.com>
To:	"Jean Delvare" <khali@...ux-fr.org>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	i2c@...sensors.org
Subject: Re: qestion about I2C_CLASS_HWMON flag

Good morning Jean,

On Thu, Sep 4, 2008 at 12:08 PM, Jean Delvare <khali@...ux-fr.org> wrote:
> In general they can, yes (where they can't, it's due to restrictions in
> protocol implementations, not device types.) But this isn't a matter of
> what devices can be on the bus. This is a matter of what devices can be
> probed for on a given bus. For example, hardware monitoring drivers
> which handle I2C devices, make sure that I2C_CLASS_HWMON is set before
> probing I2C addresses on a given bus in search of a device to
> auto-detect. On the other hand, if they are merely attaching to an I2C
> device which has already been instantiated (and thus no probing is
> needed) they do not care about the class. The reason for this mechanism
> is that probing can be risky, so we want to limit it to what is
> strictly needed. For example, there is no point in probing the I2C bus
> of a TV adapter for hardware monitoring chips - there simply can't be
> any there. If there ever was any, that would be such a special case
> that we would instantiate the I2C device in question explicitly from
> the adapter code, so we have no need for probing.

OK but which devices that can be connected to an I2C bus is platform specific,
isn't it ? For example, an I2C adapter can be used in a TV and in that
case there
may be no point to probe for a HW mon chips but this same I2C adapter can be
used by other platforms in a different context where there's a HW mon chip.

So the flags probably are useful, but they're are hard coded in adapters...

Sorry if I'm still missing something.
-- 
Francis
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