[PATCH] mtd: mxc_nand: Set timing for v2 controllers

[Sascha Hauer]

So far we relied on reset default or the bootloader to configure a
suitable clk rate for the Nand controller. This works but we can
optimize the timing for better performance. This sets the clk rate for
v2 controllers (i.MX25/35) based on the timing mode read from the ONFI
parameter page. This may also enable the symmetric mode (aks EDO mode)
if necessary which reads one word per clock cycle.
Tested on an i.MX25 with a Micron MT29F4G08ABBDAHC attached.

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 drivers/mtd/nand/mxc_nand.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
index 5173fad..725223c 100644
--- a/drivers/mtd/nand/mxc_nand.c
+++ b/drivers/mtd/nand/mxc_nand.c
@@ -1012,6 +1012,45 @@ static void preset_v1(struct mtd_info *mtd)
 	writew(0x4, NFC_V1_V2_WRPROT);
 }
 
+static void mxc_nand_v2_set_timing(struct mtd_info *mtd, uint16_t *config1)
+{
+	struct nand_chip *nand_chip = mtd->priv;
+	struct mxc_nand_host *host = nand_chip->priv;
+	int mode, ret, tRC_min_ns;
+	unsigned long rate;
+	const struct nand_sdr_timings *timings;
+
+	mode = onfi_get_async_timing_mode(nand_chip);
+	if (mode == ONFI_TIMING_MODE_UNKNOWN)
+		return;
+
+	mode = fls(mode) - 1;
+	if (mode < 0)
+		mode = 0;
+
+	timings = onfi_async_timing_mode_to_sdr_timings(mode);
+	if (IS_ERR(timings))
+		return;
+
+	tRC_min_ns = timings->tRC_min / 1000;
+	rate = 1000000000 / tRC_min_ns;
+
+	if (clk_round_rate(host->clk, rate) > 33333333)
+		/*
+		 * If tRC is smaller than 30ns (that is, the rate is higher
+		 * than 33.333MHz) we have to use EDO timing.
+		 */
+		*config1 |= NFC_V2_CONFIG1_ONE_CYCLE;
+	else
+		/* Otherwise we have two clock cycles per access. */
+		rate *= 2;
+
+	ret = clk_set_rate(host->clk, rate);
+	if (ret)
+		/* Don't worry, continue with old rate */
+		dev_err(host->dev, "failed to set clk rate: %d\n", ret);
+}
+
 static void preset_v2(struct mtd_info *mtd)
 {
 	struct nand_chip *nand_chip = mtd_to_nand(mtd);
@@ -1020,6 +1059,8 @@ static void preset_v2(struct mtd_info *mtd)
 
 	config1 |= NFC_V2_CONFIG1_FP_INT;
 
+	mxc_nand_v2_set_timing(mtd, &config1);
+
 	if (!host->devtype_data->irqpending_quirk)
 		config1 |= NFC_V1_V2_CONFIG1_INT_MSK;
 
-- 
2.8.1