ok, i obtained the physical addresses by quering the fixed information from each framebuffer
ioctl (fbdev[0], FBIOGET_FSCREENINFO, &fixed_info);
smem_start[0]=fixed_info.smem_start;
ioctl (fbdev[1], FBIOGET_FSCREENINFO, &fixed_info);
smem_start[1]=fixed_info.smem_start;
phys address of fb0...