Regression detecting memory size on PPC440EPx

Valentine vbarshak at
Tue Oct 6 02:44:53 EST 2009

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.


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:
>> 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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