IO_START
dst_pgd = pgd_offset(mm, IO_START);
flush_tlb_range(&vma, IO_START, IO_START + IO_SIZE);
#define palette_setpixel(p) *(unsigned long *)(IO_START+0x00400000) = 0x10000000|((p) & 255)
#define palette_write(v) *(unsigned long *)(IO_START+0x00400000) = 0x00000000|((v) & 0x00ffffff)
.pfn = __phys_to_pfn(IO_START),