fbmem_readback
if (!fbmem_readback(fb, 0x800000, patt)) {
if (fbmem_readback(fb, 0x800000, patt))
(!fbmem_readback(fb, 0x1000000, ++patt) ||
!fbmem_readback(fb, 0, ++patt)))
!fbmem_readback(fb, 0x800000, ++patt))
if (!fbmem_readback(fb, 0x400000, ++patt))