[U-Boot] way to determine board dram size in boot script?

Is there a recommended way to determine a board's dram size in a boot script?

I need to pass in some specific kernel parameters for a GPU driver memory allocation on boards below a certain amount of memory. I can always do a:

char str[6]; sprintf(str, "%d", (int) (gd->ram_size >> 20)); setenv("mem_mb", str);

But I was hoping there was something already out there that I didn't know about.

Regards,

Tim