Re: Regression detecting memory size on PPC440EPx

AFAIK, u-boot just writes pre-defined values to the memory controller 
registers. It doesn't do any chiptype/memsize detection. These values 
are set for Sequoia and may not suite your board. So you probably need 
to adjust the u-boot to make linux detect the memory size correctly.

Thanks,
Val.

Mikhail Zolotaryov wrote:

Hi Mike,

Address width calculation is based on the DDR-controller configuration 
set by the bootloader. It would be helpful for further discussion if you 
could send DDR0_00..DDR0_44 register values and memory configuration 
used (no of banks, bank size, I/O width) to check calculations. Thanks.

P.S. Sequoia board also has DDR2 SDRAM from Micron.

Best regards,
Mikhail Zolotaryov


Mike Nuss wrote:

quoted

There was a fix a while back called "Correct memory size calculation for
Denali based boards" that corrected the data width detection in the 4xx
bootwrapper.

This seems to have had the unintended consequence of exposing another
bug in the same code.  I have a board very similar to Sequoia, except
that it uses a DDR2 DIMM module.  It uses a single 256MB DIMM.  After
upgrading to the latest kernel, which includes the previously mentioned
fix, U-Boot works fine, but the kernel detects 512MB instead, and of
course, the kernel panics.

The error seems to be in the calculation of row bits.  U-Boot's SPD
detection says that the DIMM uses 13 bits, but I added some printf()s to
the bootwrapper, and it is setting row to 14 instead.  I'm not too clear
on how this code works; it calculates the row bits by subtracting the
row from max_row, and maybe max_row is wrong?

It looks like the data width bug canceled out this bug before, since
these values end up changing the memory size by a factor of 2 (in
opposite directions).

Could someone with a better understanding of this code take a look?

Thanks,
Mike
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