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mtd: rawnand: sunxi: Handle the tREA > tRC / 2 case 

In non-EDO, tREA should be less than tRP to guarantee that the
controller does not sample the IO lines too early. Unfortunately, the
sunxi NAND controller does not allow us to have different values for
tRP and tREH (tRP = tREH = tRW / 2).

We have 2 options to overcome this limitation:

1/ Extend tRC to fulfil the tREA <= tRC / 2 constraint
2/ Use EDO mode (only works if timings->tRLOH > 0)

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
This commit is contained in:
Boris Brezillon 2018-12-20 15:10:47 +01:00 committed by Miquel Raynal
parent f4cb4d7b46
commit 511d05e0da
1 changed files with 19 additions and 3 deletions
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22
drivers/mtd/nand/raw/sunxi_nand.c
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@ -1442,6 +1442,20 @@ static int sunxi_nfc_setup_data_interface(struct nand_chip *nand, int csline,
if (timings->tRHW_min > (min_clk_period * 20))
min_clk_period = DIV_ROUND_UP(timings->tRHW_min, 20);
/*
* In non-EDO, tREA should be less than tRP to guarantee that the
* controller does not sample the IO lines too early. Unfortunately,
* the sunxi NAND controller does not allow us to have different
* values for tRP and tREH (tRP = tREH = tRW / 2).
*
* We have 2 options to overcome this limitation:
*
* 1/ Extend tRC to fulfil the tREA <= tRC / 2 constraint
* 2/ Use EDO mode (only works if timings->tRLOH > 0)
*/
if (timings->tREA_max > min_clk_period && !timings->tRLOH_min)
min_clk_period = timings->tREA_max;
tWB = sunxi_nand_lookup_timing(tWB_lut, timings->tWB_max,
min_clk_period);
if (tWB < 0) {
@ -1497,14 +1511,16 @@ static int sunxi_nfc_setup_data_interface(struct nand_chip *nand, int csline,
return -EINVAL;
}
sunxi_nand->timing_ctl = 0;
/*
* ONFI specification 3.1, paragraph 4.15.2 dictates that EDO data
* output cycle timings shall be used if the host drives tRC less than
* 30 ns.
* 30 ns. We should also use EDO mode if tREA is bigger than tRP.
*/
min_clk_period = NSEC_PER_SEC / real_clk_rate;
sunxi_nand->timing_ctl = ((min_clk_period * 2) < 30) ?
NFC_TIMING_CTL_EDO : 0;
if (min_clk_period * 2 < 30 || min_clk_period * 1000 < timings->tREA_max)
sunxi_nand->timing_ctl = NFC_TIMING_CTL_EDO;
return 0;
}