mtd: spi-nor: Avoid setting SRWD bit in SR if WP# signal not connected

Setting the status register write disable (SRWD) bit in the status
register (SR) with WP# signal of the flash left floating or wrongly tied to
GND (that includes internal pull-downs), will configure the SR permanently
as read-only. If WP# signal is left floating or wrongly tied to GND, avoid
setting SRWD bit while writing the SR during flash protection.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20230630142233.63585-3-amit.kumar-mahapatra@amd.com
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>

Author: Amit Kumar Mahapatra

drivers/mtd/spi-nor/core.c

@@ -2844,6 +2844,9 @@ static void spi_nor_init_flags(struct spi_nor *nor)
 	if (of_property_read_bool(np, "broken-flash-reset"))
 		nor->flags |= SNOR_F_BROKEN_RESET;
 
+	if (of_property_read_bool(np, "no-wp"))
+		nor->flags |= SNOR_F_NO_WP;
+
 	if (flags & SPI_NOR_SWP_IS_VOLATILE)
 		nor->flags |= SNOR_F_SWP_IS_VOLATILE;
 

drivers/mtd/spi-nor/core.h

@@ -132,6 +132,7 @@ enum spi_nor_option_flags {
 	SNOR_F_SWP_IS_VOLATILE	= BIT(13),
 	SNOR_F_RWW		= BIT(14),
 	SNOR_F_ECC		= BIT(15),
+	SNOR_F_NO_WP		= BIT(16),
 };
 
 struct spi_nor_read_command {

drivers/mtd/spi-nor/debugfs.c

@@ -27,6 +27,7 @@ static const char *const snor_f_names[] = {
 	SNOR_F_NAME(SWP_IS_VOLATILE),
 	SNOR_F_NAME(RWW),
 	SNOR_F_NAME(ECC),
+	SNOR_F_NAME(NO_WP),
 };
 #undef SNOR_F_NAME
 

drivers/mtd/spi-nor/swp.c

@@ -214,8 +214,13 @@ static int spi_nor_sr_lock(struct spi_nor *nor, loff_t ofs, uint64_t len)
 
 	status_new = (status_old & ~mask & ~tb_mask) | val;
 
-	/* Disallow further writes if WP pin is asserted */
-	status_new |= SR_SRWD;
+	/*
+	 * Disallow further writes if WP# pin is neither left floating nor
+	 * wrongly tied to GND (that includes internal pull-downs).
+	 * WP# pin hard strapped to GND can be a valid use case.
+	 */
+	if (!(nor->flags & SNOR_F_NO_WP))
+		status_new |= SR_SRWD;
 
 	if (!use_top)
 		status_new |= tb_mask;