[PATCH v2 1/4] mtd: spi-nor-core: Do not start or end writes at odd address in DTR mode

[Manorit Chawdhry]

From: Pratyush Yadav <p.ya...@ti.com>

On DTR capable flashes like Micron Xcella the writes cannot start or end
at an odd address in DTR mode. Extra 0xff bytes need to be prepended or
appended respectively to make sure both the start and end addresses are
even.

Signed-off-by: Pratyush Yadav <p.ya...@ti.com>
Signed-off-by: Apurva Nandan <a-nan...@ti.com>
Signed-off-by: Vignesh Raghavendra <vigne...@ti.com>
Tested-by: Jonathan Humphreys <j-humphr...@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawd...@ti.com>
---
 drivers/mtd/spi/spi-nor-core.c | 59 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 55 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 982dd251150d..aea611fef523 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -1804,11 +1804,62 @@ static int spi_nor_write(struct mtd_info *mtd, loff_t 
to, size_t len,
                if (ret < 0)
                        return ret;
 #endif
+
                write_enable(nor);
-               ret = nor->write(nor, addr, page_remain, buf + i);
-               if (ret < 0)
-                       goto write_err;
-               written = ret;
+
+               /*
+                * On DTR capable flashes like Micron Xcella the writes cannot
+                * start or end at an odd address in DTR mode. So we need to
+                * append or prepend extra 0xff bytes to make sure the start
+                * address and end address are even.
+                */
+               if (spi_nor_protocol_is_dtr(nor->write_proto) &&
+                   ((addr | page_remain) & 1)) {
+                       u_char *tmp;
+                       size_t extra_bytes = 0;
+
+                       tmp = kmalloc(nor->page_size, 0);
+                       if (!tmp) {
+                               ret = -ENOMEM;
+                               goto write_err;
+                       }
+
+                       /* Prepend a 0xff byte if the start address is odd. */
+                       if (addr & 1) {
+                               tmp[0] = 0xff;
+                               memcpy(tmp + 1, buf + i, page_remain);
+                               addr--;
+                               page_remain++;
+                               extra_bytes++;
+                       } else {
+                               memcpy(tmp, buf + i, page_remain);
+                       }
+
+                       /* Append a 0xff byte if the end address is odd. */
+                       if ((addr + page_remain) & 1) {
+                               tmp[page_remain + extra_bytes] = 0xff;
+                               extra_bytes++;
+                               page_remain++;
+                       }
+
+                       ret = nor->write(nor, addr, page_remain, tmp);
+
+                       kfree(tmp);
+
+                       if (ret < 0)
+                               goto write_err;
+
+                       /*
+                        * We write extra bytes but they are not part of the
+                        * original write.
+                        */
+                       written = ret - extra_bytes;
+               } else {
+                       ret = nor->write(nor, addr, page_remain, buf + i);
+                       if (ret < 0)
+                               goto write_err;
+                       written = ret;
+               }
 
                ret = spi_nor_wait_till_ready(nor);
                if (ret)

-- 
2.43.2