Re: Can't read DIMM SPD info (DDR2)

["Michal Zatloukal" <myxal.mxl-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Sun, 11 Sep 2011 10:09:45 +0200, Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
wrote:

> Hi Michal,
> ...
> Second preliminary note: as far as I know, memtest86 reads SPD
> information using a BIOS call, while decode-dimms gets the information
> over the SMBus, assuming that SPD EEPROMs are connected to the SMBus
> and reachable at run time. This difference in access methods can
> explain why memtest86 can see information and decode-dimms not on the
> same system.

Is there a way to do the BIOS call method in Linux? If it's a sort-of
standard way to access SPD info, would it be the one used by CPU-Z to read
the SPD info on Windows? (which does work on this HW)

> First thing to check is if the SMBus on your system is properly found
> and supported:
>
> # modprobe i2c-dev
> # i2cdetect -l
>
> On an Intel system you should see an entry like:
>
> i2c-8	smbus     	SMBus I801 adapter at 0400      	SMBus adapter

Nope. On 'buntu 10.10, I only got 5 entries (didn't write them down), none
of which said smbus. On 11.10, I get:

# i2cdetect -l
i2c-0   i2c             i915 gmbus disabled                     I2C adapter
i2c-1   i2c             i915 gmbus ssc                          I2C adapter
i2c-2   i2c             i915 GPIOB                              I2C adapter
i2c-3   i2c             i915 gmbus vga                          I2C adapter
i2c-4   i2c             i915 GPIOA                              I2C adapter
i2c-5   i2c             i915 gmbus panel                        I2C adapter
i2c-6   i2c             i915 GPIOC                              I2C adapter
i2c-7   i2c             i915 gmbus dpc                          I2C adapter
i2c-8   i2c             i915 GPIOD                              I2C adapter
i2c-9   i2c             i915 gmbus dpb                          I2C adapter
i2c-10  i2c             i915 GPIOE                              I2C adapter
i2c-11  i2c             i915 gmbus reserved                     I2C adapter
i2c-12  i2c             i915 gmbus dpd                          I2C adapter
i2c-13  i2c             i915 GPIOF                              I2C adapter
i2c-14  i2c             SDVO DDC proxy                          I2C adapter

And BTW, this is the same list I get on my "server/router/AP" (Intel
D945GSEJT nettop board running 'buntu 11.04) which is also in the same
situation (can't read SPD info).

> Then you can check if devices are seen on the bus:
>
> # i2cdetect 8
>
> If you see anything in address range 0x50 to 0x55, this is likely to be
> SPD EEPROMs. Then you have to make sure that the eeprom module is
> loaded:

   From the above list, buses 3-6 have a value 0x50 at 0x50 like so:
# i2cdetect -y 5
        0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
<snip>
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

Though that's probably irrelevant, as it's not the SMBus, if I understand
correctly.


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