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>

diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index 4fd1f8da69065442d7dfa155fbb0ac076a33fcdb..4282bc47776177cc95dfa7bed5805b403c352688 100644 (file)
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -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;
 }