Regression detecting memory size on PPC440EPx
lebon at lebon.org.ua
Tue Oct 6 02:38:40 EST 2009
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.
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
> 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?
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