linux-kernel - [PATCH 4.8 13/67] mfd: stmpe: Fix RESET regression on STMPE2401

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Date:   Thu, 24 Nov 2016 16:27:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Amelie Delaunay <amelie.delaunay@...com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Patrice Chotard <patrice.chotard@...com>,
        Lee Jones <lee.jones@...aro.org>
Subject: [PATCH 4.8 13/67] mfd: stmpe: Fix RESET regression on STMPE2401

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Linus Walleij <linus.walleij@...aro.org>

commit f40584200bc4af7aa4399635b9ac213c62a13ae7 upstream.

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: Amelie Delaunay <amelie.delaunay@...com>
Fixes: c4dd1ba355aa ("mfd: stmpe: Add reset support for all STMPE variant")
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Acked-by: Patrice Chotard <patrice.chotard@...com>
Signed-off-by: Lee Jones <lee.jones@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/mfd/stmpe.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/mfd/stmpe.c
+++ b/drivers/mfd/stmpe.c
@@ -761,6 +761,8 @@ static int stmpe1801_reset(struct stmpe
 	if (ret < 0)
 		return ret;
 
+	msleep(10);
+
 	timeout = jiffies + msecs_to_jiffies(100);
 	while (time_before(jiffies, timeout)) {
 		ret = __stmpe_reg_read(stmpe, STMPE1801_REG_SYS_CTRL);