High Memory problem on 2.4.22 Linux, 2GB ppc card

Hi all,
I am working on a PPC Motorola card, which runs Linux 2.4.22. The
card has 2 GB onboard memory. But with use 1456 MB of the available memory. To increase the memory capacity i need to increase the used memory at least 64 MB. With CONFIG_HIGHMEM option all of the 2 GB memory can be used but, but the fc driver on the card has no high memory support, so this caused problems.
Then i saw that the memory is limited to 1456 by
#define MAX_LOW_MEM 0x5B000000 setting in pgtable.c. I tried
to increase it by 64 MB but i could only increase the value of MAX_LOW_MEM by 47 MB (1503 MB) without CONFIG_HIGHMEM option.

1)Is there any other setting that i should set other than
MAX_LOW_MEM to increase the usable memory to 1520 ?
2)I knew that the addressable physical memory without high memory
option was 1 G. How was it possible to address 1503 MB without CONFIG_HIGHMEM ? What is the max usable memory for 2.4.22 kernel?

Thanks,
Rinanir.

I want to change the MAX_LOW_MEM to 1520 MB, what other settings do i need to change? I do not want to use HIGHMEM because the Fiber channel does not support highmem. The card is 2 GB ppc. 1520 MB is enough. At the moment card works with 1456 MB MAX_LOW_MEM.

Thanks