[PATCH] mfd: stmpe: Fix RESET regression on STMPE2401

[Linus Walleij]

Since commit c4dd1ba355aae2bc3d1213da6c66c53e3c31e028
("mfd: stmpe: Add reset support for all STMPE variant")
we're resetting the STMPE expanders before use.

This caused a regression on the STMP2401 on the Nomadik
NHK8815:

stmpe-i2c 0-0043: stmpe2401 detected, chip id: 0x101
nmk-i2c 101f8000.i2c0: write to slave 0x43 timed out
nmk-i2c 101f8000.i2c0: no ack received after address transmission
stmpe-i2c 0-0044: stmpe2401 detected, chip id: 0x101
nmk-i2c 101f8000.i2c0: write to slave 0x44 timed out
nmk-i2c 101f8000.i2c0: no ack received after address transmission

It turns out that we start to poll for the reset bit to
go low again too quickly: the STMPE2401 is not yet online and
ready to be asked for the status of the RESET bit.

By introducing a 10ms delay before starting to hammer
the register for information, we get back to normal:

stmpe-i2c 0-0043: stmpe2401 detected, chip id: 0x101
stmpe-i2c 0-0044: stmpe2401 detected, chip id: 0x101

Cc: stable@xxxxxxxxxxxxxxx
Cc: Patrice Chotard <patrice.chotard@xxxxxx>
Cc: Amelie Delaunay <amelie.delaunay@xxxxxx>
Cc: Lee Jones <lee.jones@xxxxxxxxxx>
Fixes: c4dd1ba355aa ("mfd: stmpe: Add reset support for all STMPE variant")
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
 drivers/mfd/stmpe.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/mfd/stmpe.c b/drivers/mfd/stmpe.c
index cfdae8a3d779..b0c7bcdaf5df 100644
--- a/drivers/mfd/stmpe.c
+++ b/drivers/mfd/stmpe.c
@@ -851,6 +851,8 @@ static int stmpe_reset(struct stmpe *stmpe)
 	if (ret < 0)
 		return ret;
 
+	msleep(10);
+
 	timeout = jiffies + msecs_to_jiffies(100);
 	while (time_before(jiffies, timeout)) {
 		ret = __stmpe_reg_read(stmpe, stmpe->regs[STMPE_IDX_SYS_CTRL]);
-- 
2.7.4