[PATCH] mtd: rawnand: gpmi: Set WAIT_FOR_READY timeout based on program/erase times

[Sascha Hauer <s.hauer@pengutronix.de>]

06781a5026350 Fixes the calculation of the DEVICE_BUSY_TIMEOUT register
value from busy_timeout_cycles. busy_timeout_cycles is calculated wrong
though: It is calculated based on the maximum page read time, but the
timeout is also used for page write and block erase operations which
require orders of magnitude bigger timeouts.

Fix this by calculating busy_timeout_cycles from the maximum of
tBERS_max and tPROG_max.

This is for now the easiest and most obvious way to fix the driver.
There's room for improvements though: The NAND_OP_WAITRDY_INSTR tells us
the desired timeout for the current operation, so we could program the
timeout dynamically for each operation instead of setting a fixed
timeout. Also we could wire up the interrupt handler to actually detect
and forward timeouts occurred when waiting for the chip being ready.

As a sidenote I verified that the change in 06781a5026350 is really
correct. I wired up the interrupt handler in my tree and measured the
time between starting the operation and the timeout interrupt handler
coming in. The time increases 41us with each step in the timeout
register which corresponds to 4096 clock cycles with the 99MHz clock
that I have.

Fixes: 06781a5026350 ("mtd: rawnand: gpmi: Fix setting busy timeout setting")
Fixes: b1206122069aa ("mtd: rawniand: gpmi: use core timings instead of an empirical derivation")
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
index 889e403299568..93da23682d862 100644
--- a/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c
@@ -850,9 +850,10 @@ static int gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
 	unsigned int tRP_ps;
 	bool use_half_period;
 	int sample_delay_ps, sample_delay_factor;
-	u16 busy_timeout_cycles;
+	unsigned int busy_timeout_cycles;
 	u8 wrn_dly_sel;
 	unsigned long clk_rate, min_rate;
+	u64 busy_timeout_ps;
 
 	if (sdr->tRC_min >= 30000) {
 		/* ONFI non-EDO modes [0-3] */
@@ -885,7 +886,8 @@ static int gpmi_nfc_compute_timings(struct gpmi_nand_data *this,
 	addr_setup_cycles = TO_CYCLES(sdr->tALS_min, period_ps);
 	data_setup_cycles = TO_CYCLES(sdr->tDS_min, period_ps);
 	data_hold_cycles = TO_CYCLES(sdr->tDH_min, period_ps);
-	busy_timeout_cycles = TO_CYCLES(sdr->tWB_max + sdr->tR_max, period_ps);
+	busy_timeout_ps = max(sdr->tBERS_max, sdr->tPROG_max);
+	busy_timeout_cycles = TO_CYCLES(busy_timeout_ps, period_ps);
 
 	hw->timing0 = BF_GPMI_TIMING0_ADDRESS_SETUP(addr_setup_cycles) |
 		      BF_GPMI_TIMING0_DATA_HOLD(data_hold_cycles) |
-- 
2.30.2