With STM32 QSPI, it is possible to poll the status register of the device.
This could be done to offload the CPU during an operation (erase or
program a SPI NAND for example).

spi_mem_poll_status API has been added to handle this feature.
This new function take care of the offload/non-offload cases.

For the non-offload case, use read_poll_timeout() to poll the status in
order to release CPU during this phase.
For example, previously, when erasing large area, in non-offload case,
CPU load can reach ~50%, now it decrease to ~35%.
Signed-off-by: NPatrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: NChristophe Kerello <christophe.kerello@foss.st.com>
Reviewed-by: NBoris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/r/20210518162754.15940-2-patrice.chotard@foss.st.comSigned-off-by: NMark Brown <broonie@kernel.org>