The poll bit of the generic FIFO is used to continuously read the status of SPI device until it matches with the value in the POLL_DATA field of the poll register. The data read from the SPI device is written into the RXFIFO.
When two flash devices are used, the Quad-SPI controller does not execute the next command until the data from both flash devices matches with the value in the POLL_DATA of the poll register, which is determined by the mask bits.
The poll bit is useful when checking the status of a flash device. For example, when a page program is issued to a flash device, the software polls the status, to check if write is completed. The polling requires multiple read requests to status register. By setting the poll bit 1, the generic Quad-SPI controller continuously reads the data and checks the expected status bits.