mtd: spi-nor: add an API to restore the status of SPI flash chip

Add this API to restore the status of SPI flash chip to the default
such as addressing mode, whenever detach the driver from device or
reboot the system.

Signed-off-by: Hou Zhiqiang <[e-mail]>
Signed-off-by: Cyrille Pitchen <[e-mail]>

Documentation/mtd/spi-nor.txt

···
 initialize the necessary fields for spi_nor{}. Please see
 drivers/mtd/spi-nor/spi-nor.c for detail. Please also refer to fsl-quadspi.c
 when you want to write a new driver for a SPI NOR controller.
+Another API is spi_nor_restore(), this is used to restore the status of SPI
+flash chip such as addressing mode. Call it whenever detach the driver from
+device or reboot the system.

drivers/mtd/spi-nor/spi-nor.c

···
 		dev_err(dev, "resume() failed\n");
 }
 
+void spi_nor_restore(struct spi_nor *nor)
+{
+	/* restore the addressing mode */
+	if ((nor->addr_width == 4) &&
+	    (JEDEC_MFR(nor->info) != SNOR_MFR_SPANSION) &&
+	    !(nor->info->flags & SPI_NOR_4B_OPCODES))
+		set_4byte(nor, nor->info, 0);
+}
+EXPORT_SYMBOL_GPL(spi_nor_restore);
+
 int spi_nor_scan(struct spi_nor *nor, const char *name,
 		 const struct spi_nor_hwcaps *hwcaps)
 {

include/linux/mtd/spi-nor.h

···
 int spi_nor_scan(struct spi_nor *nor, const char *name,
 		 const struct spi_nor_hwcaps *hwcaps);
 
+/**
+ * spi_nor_restore_addr_mode() - restore the status of SPI NOR
+ * @nor:	the spi_nor structure
+ */
+void spi_nor_restore(struct spi_nor *nor);
+
 #endif