Re: Poulsbo I2C - /dev/i2c not seen when loading i2c-dev

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

On Thu, 31 Mar 2011 18:07:26 -0400, simon-wM4F9T/ekXmXDw4h08c5KA@public.gmane.org wrote:
> Hi all,
> I'm hoping that someone here can help. I am trying to get userland access
> to the I2C bus(es) on an embedded system, however recent kernels (ie.
> 2.6.38) are not 'loading' any buses when I 'modprobe i2c-dev'.
> 
> Going back to “2.6.32” I am able to see 1 bus, and 'i2cdetect 0' shows a

This is a problem on your system and not a general issue with i2c-dev
in kernel 2.6.38. i2c-dev merely creates the device nodes in /dev, it
doesn't create the buses themselves. So, if loading i2c-dev doesn't
create the device nodes, odds are that the i2c buses are missing in the
first place. Check in /sys/bus/i2c.

> single device sitting at address 0x69 (which I believe to EEPROM on the
> wifi card... not confirmed).

Very unlikely. EEPROMs typically live in the 0x50-0x57 address range.
At 0x69 is almost always a clock chip.

> The board is built around the Poulsbo and therefore using the 'i2c-isch'
> driver.

Check for error messages when you load the i2c-isch driver. Note that
in kernel 2.6.34 the structure of the i2c-isch driver was changed, from
a standalone PCI driver to a MFD driver. Please make sure that you have
CONFIG_LPC_SCH installed and driver lpc_sch loaded, otherwise i2c-isch
will never see the platform device it is looking for.

> 
> Reviewing the schematic I see that there are several buses, each going to
> individual components:
> IT8516 U5/110+111 -> LTC1760 U6/18+22 [battery charger – 0x1A/0x12]
> IT8516 U5/115+116 -> W83L771 U60/8+7 [thermal sensor – 0x18??]
> IT8516 U5/117+118 -> LSM303DLH U64/19+20 [accel/compass – 0x19]
> POULSBO U2/G37+H38 -> PCI Express Socket

This suggests that the board uses the SMBus controllers in the ITE IT8516
Super-I/O chip rather than the Intel SCH south bridge. Unfortunately we
have no support for the SMBus controllers of the IT8516, and I doubt we
get support anytime soon as I was unable to find a datasheet for the
ITE IT8516.

> I am a little dismayed by the comment in 'i2c-isch.c' which suggest it can
> handle only one i2c bus at any time.
> --
> /*
>    Supports:
> 	Intel SCH chipsets (AF82US15W, AF82US15L, AF82UL11L)
>    Note: we assume there can only be one device, with one SMBus interface.
> */
> --

This is a limitation due to the driver design. The i2c-i801 driver has
a similar limitation, but is was solved when needed:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=0cd96eb0a74791cacb27ace902b991cfd0e72abe

But according to the information you provided above, this is all
irrelevant anyway, as the Intel SCH SMBus isn't used on your system
(other than for a clock chip you do not care about.)

> 
> This seems to correlate to these comments:
> http://www.linuxforums.org/forum/programming-scripting/175147-smbus-intel-sch-us15w.html

I can't see anything interesting in this post.

> Can anyone confirm whether this is actually the case, and whether it is
> possible to configure it to use a different controller address. One would
> expect this to be a module option I guess, however it doesn't seem to take
> any.

A module option to specify an address? Come on, ISA sound cards are
gone! :p

-- 
Jean Delvare