mtd: spi-nor: ignore errors in spi_nor_unlock_all()

[ Upstream commit bdb1a75 ]

Just try to unlock the whole SPI-NOR flash array. Don't abort the
probing in case of an error. Justifications:
 (1) For some boards, this just works because
     spi_nor_write_16bit_sr_and_check() is broken and just checks the
     second half of the 16bit. Once that will be fixed, SPI probe will
     fail for boards which has hardware-write protected SPI-NOR flashes.
 (2) Until now, hardware write-protection was the only viable solution
     to use the block protection bits. This is because this very
     function spi_nor_unlock_all() will be called unconditionally on
     every linux boot. Therefore, this bits only makes sense in
     combination with the hardware write-protection. If we would fail
     the SPI probe on an error in spi_nor_unlock_all() we'd break
     virtually all users of the block protection bits.
 (3) We should try hard to keep the MTD working even if the flash might
     not be writable/erasable.

Fixes: 3e0930f ("mtd: spi-nor: Rework the disabling of block write protection")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20201203162959.29589-3-michael@walle.cc
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/mtd/spi-nor/core.c

@@ -2915,20 +2915,27 @@ static int spi_nor_quad_enable(struct spi_nor *nor)
 }
 
 /**
- * spi_nor_unlock_all() - Unlocks the entire flash memory array.
+ * spi_nor_try_unlock_all() - Tries to unlock the entire flash memory array.
  * @nor:	pointer to a 'struct spi_nor'.
  *
  * Some SPI NOR flashes are write protected by default after a power-on reset
  * cycle, in order to avoid inadvertent writes during power-up. Backward
  * compatibility imposes to unlock the entire flash memory array at power-up
  * by default.
+ *
+ * Unprotecting the entire flash array will fail for boards which are hardware
+ * write-protected. Thus any errors are ignored.
  */
-static int spi_nor_unlock_all(struct spi_nor *nor)
+static void spi_nor_try_unlock_all(struct spi_nor *nor)
 {
-	if (nor->flags & SNOR_F_HAS_LOCK)
-		return spi_nor_unlock(&nor->mtd, 0, nor->params->size);
+	int ret;
 
-	return 0;
+	if (!(nor->flags & SNOR_F_HAS_LOCK))
+		return;
+
+	ret = spi_nor_unlock(&nor->mtd, 0, nor->params->size);
+	if (ret)
+		dev_dbg(nor->dev, "Failed to unlock the entire flash memory array\n");
 }
 
 static int spi_nor_init(struct spi_nor *nor)
@@ -2941,11 +2948,7 @@ static int spi_nor_init(struct spi_nor *nor)
 		return err;
 	}
 
-	err = spi_nor_unlock_all(nor);
-	if (err) {
-		dev_dbg(nor->dev, "Failed to unlock the entire flash memory array\n");
-		return err;
-	}
+	spi_nor_try_unlock_all(nor);
 
 	if (nor->addr_width == 4 && !(nor->flags & SNOR_F_4B_OPCODES)) {
 		/*