[PATCH] mtd: nand: Fix writing mtdoops to nand flash

[motobud@gmail.com]

From: Brent Taylor <motobud@gmail.com>

Gregg,
  I apologize for the 4.4.y patch, I screwed up the branching 
in my local tree and tried to submit one patch that would cover 
versions 4.4.y and 3.18.y.  Here is a valid 4.4.y patch.
  -- Brent

commit 30863e38ebeb500a31cecee8096fb5002677dd9b upstream.

When mtdoops calls mtd_panic_write(), it eventually calls
panic_nand_write() in nand_base.c. In order to properly wait for the
nand chip to be ready in panic_nand_wait(), the chip must first be
selected.

When using the atmel nand flash controller, a panic would occur due to
a NULL pointer exception.

Fixes: 2af7c6539931 ("mtd: Add panic_write for NAND flashes")
Cc: <stable@vger.kernel.org> # 4.4.x
Signed-off-by: Brent Taylor <motobud@gmail.com>
---
 drivers/mtd/nand/nand_base.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 54ab48827258..7ba109e8cf88 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2663,15 +2663,18 @@ static int panic_nand_write(struct mtd_info *mtd, loff_t to, size_t len,
 			    size_t *retlen, const uint8_t *buf)
 {
 	struct nand_chip *chip = mtd->priv;
+	int chipnr = (int)(to >> chip->chip_shift);
 	struct mtd_oob_ops ops;
 	int ret;
 
-	/* Wait for the device to get ready */
-	panic_nand_wait(mtd, chip, 400);
-
 	/* Grab the device */
 	panic_nand_get_device(chip, mtd, FL_WRITING);
 
+	chip->select_chip(mtd, chipnr);
+
+	/* Wait for the device to get ready */
+	panic_nand_wait(mtd, chip, 400);
+
 	memset(&ops, 0, sizeof(ops));
 	ops.len = len;
 	ops.datbuf = (uint8_t *)buf;
-- 
2.15.0