drivers: flash: spi_nor: clean up ready detection

Reads would wait until the device was ready before issuing the first
command; writes and erases did not.  Fix this documenting and changing
so that wait-for-ready is invoked only where needed, i.e. to confirm
that a WRITE_STATUS, ERASE, or PROGRAM operation has completed before
proceeding to allow more commands to be submitted.  This matches Linux
spi_nor driver behavior.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

Author: pabigot

drivers/flash/spi_nor.c

@@ -307,6 +307,32 @@ static int spi_nor_access(const struct device *const dev,
 #define spi_nor_cmd_addr_write(dev, opcode, addr, src, length) \
 	spi_nor_access(dev, opcode, true, addr, (void *)src, length, true)
 
+/**
+ * @brief Wait until the flash is ready
+ *
+ * @note The device must be externally acquired before invoking this
+ * function.
+ *
+ * This function should be invoked after every ERASE, PROGRAM, or
+ * WRITE_STATUS operation before continuing.  This allows us to assume
+ * that the device is ready to accept new commands at any other point
+ * in the code.
+ *
+ * @param dev The device structure
+ * @return 0 on success, negative errno code otherwise
+ */
+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));
+
+	return ret;
+}
+
 #if defined(CONFIG_SPI_NOR_SFDP_RUNTIME) || defined(CONFIG_FLASH_JESD216_API)
 /*
  * @brief Read content from the SFDP hierarchy
@@ -430,24 +456,6 @@ static void release_device(const struct device *dev)
 	}
 }
 
-/**
- * @brief Wait until the flash is ready
- *
- * @param dev The device structure
- * @return 0 on success, negative errno code otherwise
- */
-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, 1);
-	} while (!ret && (reg & SPI_NOR_WIP_BIT));
-
-	return ret;
-}
-
 static int spi_nor_read(const struct device *dev, off_t addr, void *dest,
 			size_t size)
 {
@@ -461,8 +469,6 @@ static int spi_nor_read(const struct device *dev, off_t addr, void *dest,
 
 	acquire_device(dev);
 
-	spi_nor_wait_until_ready(dev);
-
 	ret = spi_nor_cmd_addr_read(dev, SPI_NOR_CMD_READ, addr, dest, size);
 
 	release_device(dev);
@@ -600,8 +606,6 @@ static int spi_nor_write_protection_set(const struct device *dev,
 {
 	int ret;
 
-	spi_nor_wait_until_ready(dev);
-
 	ret = spi_nor_cmd_write(dev, (write_protect) ?
 	      SPI_NOR_CMD_WRDI : SPI_NOR_CMD_WREN);
 
@@ -621,8 +625,6 @@ static int spi_nor_sfdp_read(const struct device *dev, off_t addr,
 {
 	acquire_device(dev);
 
-	spi_nor_wait_until_ready(dev);
-
 	int ret = read_sfdp(dev, addr, dest, size);
 
 	release_device(dev);
@@ -641,8 +643,6 @@ static int spi_nor_read_jedec_id(const struct device *dev,
 
 	acquire_device(dev);
 
-	spi_nor_wait_until_ready(dev);
-
 	int ret = spi_nor_cmd_read(dev, SPI_NOR_CMD_RDID, id, SPI_NOR_MAX_ID_LEN);
 
 	release_device(dev);