spi: Introduce spi-cs-setup-ns property

SPI NOR flashes have specific cs-setup time requirements without which
they can't work at frequencies close to their maximum supported frequency,
as they miss the first bits of the instruction command. Unrecognized
commands are ignored, thus the flash will be unresponsive. Introduce the
spi-cs-setup-ns property to allow spi devices to specify their cs setup
time.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20221117105249.115649-3-tudor.ambarus@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: ambarus

drivers/spi/spi.c

@@ -2224,6 +2224,7 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 			   struct device_node *nc)
 {
 	u32 value;
+	u16 cs_setup;
 	int rc;
 
 	/* Mode (clock phase/polarity/etc.) */
@@ -2309,6 +2310,11 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 	if (!of_property_read_u32(nc, "spi-max-frequency", &value))
 		spi->max_speed_hz = value;
 
+	if (!of_property_read_u16(nc, "spi-cs-setup-ns", &cs_setup)) {
+		spi->cs_setup.value = cs_setup;
+		spi->cs_setup.unit = SPI_DELAY_UNIT_NSECS;
+	}
+
 	return 0;
 }