I suspect that i have accidently set the flash chip into QPI mode after which the read ID and other read/write commands fail (0x00 returned for all reads). In QPI mode the flash expects the instruction cycle to be also in 4 lines.
From the datasheet its mentioned that 0xF5 has to be send to exit this mode. But i'm unsure as to how i can modify the qspi driver to send 1 byte in 4 lines as shown below.
Its not clear from the Zynq TRM how the bus width for the transfer is selected in I/O mode.