At present, the flow of calculating AC timing of read/write cycle in SDR
mode is that:
At first, calculate high hold time which is valid for both read and write
cycle using the max value between tREH_min and tWH_min.
Secondly, calculate WE# pulse width using tWP_min.
Thridly, calculate RE# pulse width using the bigger one between tREA_max
and tRP_min.
But NAND SPEC shows that Controller should also meet write/read cycle time.
That is write cycle time should be more than tWC_min and read cycle should
be more than tRC_min. Obviously, we do not achieve that now.
This patch corrects the low level time calculation to meet minimum
read/write cycle time required. After getting the high hold time, WE# low
level time will be promised to meet tWP_min and tWC_min requirement,
and RE# low level time will be promised to meet tREA_max, tRP_min and
tRC_min requirement.
Fixes: edfee3619c49 ("mtd: nand: mtk: add ->setup_data_interface() hook")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Xiaolei Li <xiaolei.li@xxxxxxxxxxxx>
---
drivers/mtd/nand/raw/mtk_nand.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)
diff --git a/drivers/mtd/nand/raw/mtk_nand.c b/drivers/mtd/nand/raw/mtk_nand.c
index b6b4602f5132..4fbb0c6ecae3 100644
--- a/drivers/mtd/nand/raw/mtk_nand.c
+++ b/drivers/mtd/nand/raw/mtk_nand.c
@@ -508,7 +508,8 @@ static int mtk_nfc_setup_data_interface(struct nand_chip *chip, int csline,
{
struct mtk_nfc *nfc = nand_get_controller_data(chip);
const struct nand_sdr_timings *timings;
- u32 rate, tpoecs, tprecs, tc2r, tw2r, twh, twst, trlt;
+ u32 rate, tpoecs, tprecs, tc2r, tw2r, twh, twst = 0, trlt = 0;
+ u32 thold;
timings = nand_get_sdr_timings(conf);
if (IS_ERR(timings))
@@ -544,11 +545,28 @@ static int mtk_nfc_setup_data_interface(struct nand_chip *chip, int csline,
twh = DIV_ROUND_UP(twh * rate, 1000000) - 1;
twh &= 0xf;
- twst = timings->tWP_min / 1000;
+ /* Calculate real WE#/RE# hold time in nanosecond */
+ thold = (twh + 1) * 1000000 / rate;
+ /* nanosecond to picosecond */
+ thold *= 1000;
+
+ /**
+ * WE# low level time should be expaned to meet WE# pulse time
+ * and WE# cycle time at the same time.
+ */
+ if (thold < timings->tWC_min)
+ twst = timings->tWC_min - thold;
+ twst = max(timings->tWP_min, twst) / 1000;
twst = DIV_ROUND_UP(twst * rate, 1000000) - 1;
twst &= 0xf;
- trlt = max(timings->tREA_max, timings->tRP_min) / 1000;
+ /**
+ * RE# low level time should be expaned to meet RE# pulse time,
+ * RE# access time and RE# cycle time at the same time.
+ */
+ if (thold < timings->tRC_min)
+ trlt = timings->tRC_min - thold;
+ trlt = max3(trlt, timings->tREA_max, timings->tRP_min) / 1000;
trlt = DIV_ROUND_UP(trlt * rate, 1000000) - 1;
trlt &= 0xf;
--
2.18.0
