[lm-sensors] [v4l-dvb-maintainer] Re: [PATCH 1/3] i2c: allow

[abraham.manu@gmail.com (Manu Abraham)]

Hi All,

Nathan Lutchansky wrote:
>
> At the moment, anyway.  It will become more and more necessary as the
> number of different I2C sensor chips on the market increases.  V4L/DVB has 
> already hit this problem in a big way.
>
>   


DVB doesn't probe for i2c devices. The DVB adapter, ie the card knows 
what devices that are present and works under that assumption.

Earlier DVB had the problem with probing. ie a different device is found 
at the expected location of another device(In the case of probing) and 
this device doesn't like to be fiddled around with. And "lo" we have a 
perfect freeze.

After many such cases, DVB no longer probes for i2c devices (we now 
longer have anymore i2c issues)
V4L on the other hand probes for all devices. This is IMHO wrong, due to

(1) When the probe list grows long, it takes longer time for the probe 
to succeed (V4L guys themselves would agree to the fact that they have 
seen probes in the order of ~30 minutes ! Yuck)

(2) Probing wrong devices

So in any case probing can never be right, unless the card information 
is passed to the i2c core. But in that sense it is no longer a probe. It 
is indeed just an attach method. In that case, it makes no sense to make 
i2c core go around in circles.

The proper way to handle this, is that only the right device is 
attached. Rather than making i2c to do this, subsystems should be 
handling this.


my 2 cents


Manu