mtd: nand: return consistent error codes in ecc.correct() implementations

The error code returned by the ecc.correct() are not consistent over the
all implementations.

Document the expected behavior in include/linux/mtd/nand.h and fix
offending implementations.

[Brian: this looks like a bugfix for the ECC reporting in the bf5xx_nand
driver, but we haven't seen any testing results for it]

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Franklin S Cooper Jr. <fcooper@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

2 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 3e92be1d2d43..518958115182 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -456,7 +456,13 @@ struct nand_hw_control {
  * @hwctl:      function to control hardware ECC generator. Must only
  *              be provided if an hardware ECC is available
  * @calculate:  function for ECC calculation or readback from ECC hardware
- * @correct:    function for ECC correction, matching to ECC generator (sw/hw)
+ * @correct:    function for ECC correction, matching to ECC generator (sw/hw).
+ *              Should return a positive number representing the number of
+ *              corrected bitflips, -EBADMSG if the number of bitflips exceed
+ *              ECC strength, or any other error code if the error is not
+ *              directly related to correction.
+ *              If -EBADMSG is returned the input buffers should be left
+ *              untouched.
  * @read_page_raw:      function to read a raw page without ECC. This function
  *                      should hide the specific layout used by the ECC
  *                      controller and always return contiguous in-band and
diff --git a/include/linux/mtd/nand_bch.h b/include/linux/mtd/nand_bch.h
index 74acf5367556..fb0bc3420a10 100644
--- a/include/linux/mtd/nand_bch.h
+++ b/include/linux/mtd/nand_bch.h
@@ -55,7 +55,7 @@ static inline int
 nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
                       unsigned char *read_ecc, unsigned char *calc_ecc)
 {
-        return -1;
+        return -ENOTSUPP;
 }
 
 static inline struct nand_bch_control *