flash: spi_nor: don't hard loop in wait_until_ready

Don't monopolise the CPU in `spi_nor_wait_until_ready`. For slow flash
chips, operations can take minutes (Full chip erase on MX25R is listed
as 120s typical, 240s max).

Signed-off-by: Jordan Yates <[email protected]>

Author: Jordan Yates

drivers/flash/Kconfig.nor

@@ -55,6 +55,16 @@ config SPI_NOR_CS_WAIT_DELAY
 	help
 	  This is the wait delay (in us) to allow for CS switching to take effect
 
+config SPI_NOR_SLEEP_WHILE_WAITING_UNTIL_READY
+	bool "Sleep while waiting for flash operations to complete"
+	default y
+	help
+	  Flash operations can take anywhere from 1ms to 240 seconds to
+	  complete. Enabling this option adds a delay between polls on the
+	  status register for slow operations. Disabling this option can
+	  result in significant flash savings if this driver is the only user
+	  of "k_sleep". This can be the case when building as a bootloader.
+
 config SPI_NOR_FLASH_LAYOUT_PAGE_SIZE
 	int "Page size to use for FLASH_LAYOUT feature"
 	default 65536

drivers/flash/spi_nor.c

@@ -402,10 +402,19 @@ static int spi_nor_wait_until_ready(const struct device *dev)
 	int ret;
 	uint8_t reg;
 
-	do {
-		ret = spi_nor_cmd_read(dev, SPI_NOR_CMD_RDSR, &reg, sizeof(reg));
-	} while (!ret && (reg & SPI_NOR_WIP_BIT));
+	ARG_UNUSED(poll_delay);
 
+	while (true) {
+		ret = spi_nor_cmd_read(dev, SPI_NOR_CMD_RDSR, &reg, sizeof(reg));
+		/* Exit on error or no longer WIP */
+		if (ret || !(reg & SPI_NOR_WIP_BIT)) {
+			break;
+		}
+#ifdef CONFIG_SPI_NOR_SLEEP_WHILE_WAITING_UNTIL_READY
+		/* Don't monopolise the CPU while waiting for ready */
+		k_sleep(K_TICKS(1));
+#endif /* CONFIG_SPI_NOR_SLEEP_WHILE_WAITING_UNTIL_READY */
+	}
 	return ret;
 }