[PATCH 4/4] mtd: rawnand: fsmc: Fix timing computation

[Herve Codina <herve.codina@bootlin.com>]

The timing setting were incorrect on some nands leading to a
fallback to mode 0 timing on some Micron nand or to incorrect
data reads on some Winbond NAND.

The timing computation did not take into account the following
constraint given in SPEAr3xx reference manual:
  twait >= tCEA - tset*TCLK + TOUTDEL + TINDEL

This patch adds this constraint and fixes the issues on both
nands having the both nands working at mode 3 timing.
The change has no impact on slower timing mode such as mode 0.
Indeed, on mode 0 timing, computed values are the same with and
without the patch.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/mtd/nand/raw/fsmc_nand.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/mtd/nand/raw/fsmc_nand.c b/drivers/mtd/nand/raw/fsmc_nand.c
index bff09219ce3a..a3aa66f30869 100644
--- a/drivers/mtd/nand/raw/fsmc_nand.c
+++ b/drivers/mtd/nand/raw/fsmc_nand.c
@@ -278,7 +278,7 @@ static int fsmc_calc_timings(struct fsmc_nand_data *host,
 {
 	unsigned long hclk = clk_get_rate(host->clk);
 	unsigned long hclkn = NSEC_PER_SEC / hclk;
-	u32 thiz, thold, twait, tset;
+	u32 thiz, thold, twait, tset, tmp;
 
 	if (sdrt->tRC_min < 30000)
 		return -EOPNOTSUPP;
@@ -310,13 +310,6 @@ static int fsmc_calc_timings(struct fsmc_nand_data *host,
 	else if (tims->thold > FSMC_THOLD_MASK)
 		tims->thold = FSMC_THOLD_MASK;
 
-	twait = max(sdrt->tRP_min, sdrt->tWP_min);
-	tims->twait = DIV_ROUND_UP(twait / 1000, hclkn) - 1;
-	if (tims->twait == 0)
-		tims->twait = 1;
-	else if (tims->twait > FSMC_TWAIT_MASK)
-		tims->twait = FSMC_TWAIT_MASK;
-
 	tset = max(sdrt->tCS_min - sdrt->tWP_min,
 		   sdrt->tCEA_max - sdrt->tREA_max);
 	tims->tset = DIV_ROUND_UP(tset / 1000, hclkn) - 1;
@@ -325,6 +318,24 @@ static int fsmc_calc_timings(struct fsmc_nand_data *host,
 	else if (tims->tset > FSMC_TSET_MASK)
 		tims->tset = FSMC_TSET_MASK;
 
+	twait = max(sdrt->tRP_min, sdrt->tWP_min);
+
+	/* According to SPEAr300 Reference Manual (RM0082) which gives more
+	 * information related to FSMSC timings than the SPEAr600 one (RM0305),
+	 *   twait >= tCEA - tset*TCLK + TOUTDEL + TINDEL
+	 * With TOUTDEL = 7ns (Output delay from the flip-flops to the board)
+	 * and TINDEL = 5ns (Input delay from the board to the flipflop)
+	 */
+	tmp = sdrt->tCEA_max - (tims->tset + 1)*hclkn*1000 + 7000 + 5000;
+	if (twait < tmp)
+		twait = tmp;
+
+	tims->twait = DIV_ROUND_UP(twait / 1000, hclkn) - 1;
+	if (tims->twait == 0)
+		tims->twait = 1;
+	else if (tims->twait > FSMC_TWAIT_MASK)
+		tims->twait = FSMC_TWAIT_MASK;
+
 	return 0;
 }
 
-- 
2.31.1