Re: [PATCH v3 3/3] mtd-nand: DaVinci: Add 4-bit ECC support for large page NAND chips

[David Brownell <david-b@pacbell.net>]

On Thursday 16 July 2009, nsnehaprabha@ti.com wrote:
> 	It also fixes a bug in the ECC correction handler.
> When we introduce 5 bit-errors in chunk, error correction stops working. When
> errors are detected the 4BITECC_START bit was left high, which should be
> cleared. 

Agreed that needs to be fixed, but there should be a comment
about this being an *undocumented* behavior in the hardware.

The reason that the bug exists at all is because this step
has never been documented.  So, please roll in this update.

- Dave

---
 drivers/mtd/nand/davinci_nand.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -350,13 +350,16 @@ compare:
 
 	/*
 	 * Clear any previous address calculation by doing a dummy read of an
-	 * error address register.
+	 * error address register.  UNDOCUMENTED that the ECC engine won't
+	 * recover after 5-bit ECC errors without this step.
 	 */
 	davinci_nand_readl(info, NAND_ERR_ADD1_OFFSET);
 
 	/* Start address calculation, and wait for it to complete.
 	 * We _could_ start reading more data while this is working,
-	 * to speed up the overall page read.
+	 * to speed up the overall page read.  UNDOCUMENTED that
+	 * reading some ERRVAL register is needed in all cases, not
+	 * just when an error must be corrected.
 	 */
 	davinci_nand_writel(info, NANDFCR_OFFSET,
 			davinci_nand_readl(info, NANDFCR_OFFSET) | BIT(13));