[PATCH v2] mtd: spinand: Do not update the QE bit on devices without one

[Sagnik Sasmal]

Commit be0b86c648bf ("mtd: spinand: Gather all the bus interface
steps in one single function") moved quad-enable setup into
spinand_configure_chip(). The new code only determines whether quad
mode is needed when SPINAND_HAS_QE_BIT is set, but calls
spinand_init_quad_enable() unconditionally. This clears configuration
register bit 0 on devices without a QE bit.

That bit is not universally a QE bit. On the Winbond W25N02KV it is
H-DIS, which disables the active-low HOLD function. Clearing H-DIS
enables HOLD during single and dual I/O operations. If IO3 is not kept
high, the flash can pause a command and ignore clock and data.

H-DIS is not restored by the FFh reset command, allowing the incorrect
state to survive an SoC warm reboot while the flash remains powered.

Before the refactoring, spinand_init_quad_enable() returned without
touching the configuration register on devices without
SPINAND_HAS_QE_BIT. Restore that behavior by only calling the helper
when the flag is set.

The regression was reproduced on a JioRouter JIDU6401 with an MT7986
SoC and a W25N02KV. With Linux 6.18.44, sysupgrade failed and the
following warm reboot hung in BL2. With this change applied, both
sysupgrade and warm reboot completed successfully.

Fixes: be0b86c648bf ("mtd: spinand: Gather all the bus interface steps in one single function")
Cc: stable at vger.kernel.org
Suggested-by: Miquel Raynal <miquel.raynal at bootlin.com>
Assisted-by: LLM
Signed-off-by: Sagnik Sasmal <sagnik at sagnik.me>
---
I really appreciate the prompt review and your suggestion for a cleaner
approach. Thank you.

Changes in v2:
- Call spinand_init_quad_enable() only inside the
  SPINAND_HAS_QE_BIT condition, as suggested by Miquel.
- Retested on a JioRouter JIDU6401; sysupgrade and the following warm
  reboot completed successfully.

 drivers/mtd/nand/spi/core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
index 43bbe2629..e59581d35 100644
--- a/drivers/mtd/nand/spi/core.c
+++ b/drivers/mtd/nand/spi/core.c
@@ -1813,11 +1813,11 @@ static int spinand_configure_chip(struct spinand_device *spinand)
 		    spinand->ssdr_op_templates.write_cache->data.buswidth == 4 ||
 		    spinand->ssdr_op_templates.update_cache->data.buswidth == 4)
 			quad_enable = true;
-	}
 
-	ret = spinand_init_quad_enable(spinand, quad_enable);
-	if (ret)
-		return ret;
+		ret = spinand_init_quad_enable(spinand, quad_enable);
+		if (ret)
+			return ret;
+	}
 
 	if (spinand->configure_chip) {
 		ret = spinand->configure_chip(spinand, SSDR);
-- 
2.53.0