[PATCH v4 2/2] mtd: spi-nor: Avoid setting SRWD bit in SR if WP# signal not connected

[Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>]

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>
---
 drivers/mtd/spi-nor/core.c    | 3 +++
 drivers/mtd/spi-nor/core.h    | 1 +
 drivers/mtd/spi-nor/debugfs.c | 1 +
 drivers/mtd/spi-nor/swp.c     | 9 +++++++--
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 0bb0ad14a2fc..520f5ab86d2b 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -2864,6 +2864,9 @@ static void spi_nor_init_flags(struct spi_nor *nor)
 	if (flags & NO_CHIP_ERASE)
 		nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
 
+	if (of_property_read_bool(np, "no-wp"))
+		nor->flags |= SNOR_F_NO_WP;
+
 	if (flags & SPI_NOR_RWW && nor->info->n_banks > 1 &&
 	    !nor->controller_ops)
 		nor->flags |= SNOR_F_RWW;
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index 4fb5ff09c63a..55b5e7abce6e 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/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 {
diff --git a/drivers/mtd/spi-nor/debugfs.c b/drivers/mtd/spi-nor/debugfs.c
index e11536fffe0f..6e163cb5b478 100644
--- a/drivers/mtd/spi-nor/debugfs.c
+++ b/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
 
diff --git a/drivers/mtd/spi-nor/swp.c b/drivers/mtd/spi-nor/swp.c
index 0ba716e84377..5ab9d5324860 100644
--- a/drivers/mtd/spi-nor/swp.c
+++ b/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;
-- 
2.17.1