[PATCH] mtd: spi-nor: allow force unlocking via DT property

[Chen Minqiang <ptpt52@gmail.com>]

Some SPI NOR flash chips (such as generic or unlisted chips used in vendor
devices like Tenda AX12L Pro) have Block Protection (BP) bits set in the
Status Register by bootloaders or factory settings, locking flash blocks.

Because vendors frequently switch between various generic SPI NOR flash
chips ("Flash Lottery"), it is impractical to upstream explicit chip ID
flags (SNOR_F_HAS_LOCK) for every possible generic chip variant.

This patch introduces support for the "linux,force-sr-unlock" Device Tree
property:
1. In spi_nor_init(), trigger spi_nor_try_unlock_all() if "linux,force-sr-unlock"
   is present in the flash DT node, even when CONFIG_MTD_SPI_NOR_SWP_DISABLE_ON_VOLATILE
   is active and the chip is non-volatile.
2. In spi_nor_try_unlock_all(), bypass the SNOR_F_HAS_LOCK flag check when
   "linux,force-sr-unlock" is specified, ensure locking_ops are initialized,
   and invoke Linux kernel's native spi_nor_unlock() mechanism.

Signed-off-by: Chen Minqiang <ptpt52@gmail.com>
---
 drivers/mtd/spi-nor/core.c | 3 ++-
 drivers/mtd/spi-nor/swp.c  | 7 ++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index ccf4396cdcd0..ef0bdc1254bb 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3332,7 +3332,8 @@ static int spi_nor_init(struct spi_nor *nor)
 	spi_nor_cache_sr_lock_bits(nor, NULL);
 	if (IS_ENABLED(CONFIG_MTD_SPI_NOR_SWP_DISABLE) ||
 	    (IS_ENABLED(CONFIG_MTD_SPI_NOR_SWP_DISABLE_ON_VOLATILE) &&
-	     nor->flags & SNOR_F_SWP_IS_VOLATILE)) {
+	     nor->flags & SNOR_F_SWP_IS_VOLATILE) ||
+	    of_property_read_bool(spi_nor_get_flash_node(nor), "linux,force-sr-unlock")) {
 		spi_nor_try_unlock_all(nor);
 	}
 
diff --git a/drivers/mtd/spi-nor/swp.c b/drivers/mtd/spi-nor/swp.c
index 235070b215d1..a190d10c1630 100644
--- a/drivers/mtd/spi-nor/swp.c
+++ b/drivers/mtd/spi-nor/swp.c
@@ -628,11 +628,16 @@ static int spi_nor_is_locked(struct mtd_info *mtd, loff_t ofs, u64 len)
  */
 void spi_nor_try_unlock_all(struct spi_nor *nor)
 {
+	struct device_node *np = spi_nor_get_flash_node(nor);
+	bool force_unlock = of_property_read_bool(np, "linux,force-sr-unlock");
 	int ret;
 
-	if (!(nor->flags & SNOR_F_HAS_LOCK))
+	if (!(nor->flags & SNOR_F_HAS_LOCK) && !force_unlock)
 		return;
 
+	if (!nor->params->locking_ops)
+		spi_nor_init_default_locking_ops(nor);
+
 	dev_dbg(nor->dev, "Unprotecting entire flash array\n");
 
 	ret = spi_nor_unlock(&nor->mtd, 0, nor->params->size);
-- 
2.17.1