[lm-sensors] Configuring I2C on a Thinkpad T42

[lm-sensors] Configuring I2C on a Thinkpad T42

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Hi all,

I was hoping you might help resolve some confusion on my part regarding I2C.

I have a Thinkpad T42, and as far as I can tell, it has an Intel 82801
SMBus (which I gather from the output of lspci), and a National
Semiconductor PC87591 sensors chip (which I read at
http://archives.andrew.net.au/lm-sensors/msg31277.html).

I'm not completely new to Linux, but I don't know much about I2C,
although I've read some of the basics.  From what I understand, I2C can
be used by lm-sensors, and possibly by ACPI. 

I've read ominous things about lm-sensors in regards to Thinkpads (at
http://www.thinkwiki.org/wiki/Problem_with_lm-sensors), but I don't know
if this means that I should abandon trying to get any benefit from the
I2C bus.

Here's a few questions I have:

   1. Do I need to have the kernel configured for /both/ hardware bus
      support /and/ sensors chip support to get any value out of I2C, or
      is it possible there are other devices on the bus that might be of
      service?
   2. Is there any great way to confirm that Thinkpad T42's actually
      have a NS PC87591 sensors chip?  I was hesitant to run the
      sensors-detect on my Thinkpad because of sharp warnings I found
      on-line.
   3. If I can't use lm-sensors on a Thinkpad, does ACPI rely at all on
      I2C?  If so, what kind of configuration do I need to set that up
      (kernel-wise or user-space-wise)?
   4. How should I test that I2C is working when everything's all set up?

I appreciate any feedback you can provide, even if just pointing me
towards other resources.

Thanks,
Sukant

[lm-sensors] Configuring I2C on a Thinkpad T42

[Rudolf Marek]

Hi

> I have a Thinkpad T42, and as far as I can tell, it has an Intel 82801
> SMBus (which I gather from the output of lspci), and a National
> Semiconductor PC87591 sensors chip (which I read at
> http://archives.andrew.net.au/lm-sensors/msg31277.html).

I think we do not have the driver for this chip yet.

> I'm not completely new to Linux, but I don't know much about I2C,
> although I've read some of the basics.  From what I understand, I2C can
> be used by lm-sensors, and possibly by ACPI. 

Lm-sensors talk to chips directly. ACPI is a framework between operation system and hardware. It used for powermanagent and
also temps/fans control in notebooks.

> I've read ominous things about lm-sensors in regards to Thinkpads (at
> http://www.thinkwiki.org/wiki/Problem_with_lm-sensors), but I don't know
> if this means that I should abandon trying to get any benefit from the
> I2C bus.

There is a security EEPROM connected to i2c which will be corrupted if you scan the bus. BIOS will disallow to start the
notebook and your motherboard will need to be replaced.

> Here's a few questions I have:
> 
>    1. Do I need to have the kernel configured for /both/ hardware bus
>       support /and/ sensors chip support to get any value out of I2C, or
>       is it possible there are other devices on the bus that might be of
>       service?

You need the bus driver to talk to devices connected to a bus. You can just abstract the I2C bus as a network connected chips
every chip with some address. Each chip has some accessible registers which chip drivers understand.

>    2. Is there any great way to confirm that Thinkpad T42's actually
>       have a NS PC87591 sensors chip?  I was hesitant to run the
>       sensors-detect on my Thinkpad because of sharp warnings I found
>       on-line.


This is EXTREMLY DANGEROUS !!!!!!!!!!!!
I think you can run it ONLY IF you delete i2c-i801 module AND DO NOT ALLOW to SCAN i2c/SMBUS. (or compile kernel WITHOUT i2c bus drivers
support)

****************************************
If you will ALLOW it YOUR MOTHERBOARD IS LIKELY needed to be replaced ant it will COST you a LOT of money.
****************************************

DO NOT TRY IT if ACPI works for you.

acpi -V

should show the temps. And that is what you need ;)


>    3. If I can't use lm-sensors on a Thinkpad, does ACPI rely at all on
>       I2C?  If so, what kind of configuration do I need to set that up
>       (kernel-wise or user-space-wise)?

It may use I2C to get battery status etc... If you want to use ACPI you should configure your kernel see ACPI-HOWTO for details.

>    4. How should I test that I2C is working when everything's all set up?

Do not try to play with I2C on you thinkpad.

> I appreciate any feedback you can provide, even if just pointing me
> towards other resources.

Try google to find something about I2C you can start at Philips web site.

Regards

Rudolf