[PATCH v1] pinctrl: mcp23s08: Reset all output latches to default at probe

[bigunclemax@gmail.com]

From: "Maksim Kiselev" <bigunclemax@gmail.com>

It appears that resetting only the direction register is not sufficient,
it's also necessary to reset the OLAT register to its default values.

Otherwise, the following situation can occur:

If a pin was configured as OUT=1 before driver probe(Ex: IODIR=1,IOLAT=1),
then after loading the MCP driver, the cache will be populated from
reg_defaults with IOLAT=0 (while the actual value in the chip is 1).
A subsequent setting OUT=0 will fail because
mcp_update_bits(mcp, MCP_OLAT, ...) calls regmap_update_bits(),
which will check that the value to be set (0) matches the cached value (0)
and thus skip writing actual value to the MCP chip.

To avoid this, the OLAT register must be explicitly reset at probe.

Fixes: 3ede3f8b4b4b ("pinctrl: mcp23s08: Reset all pins to input at probe")
Signed-off-by: Maksim Kiselev <bigunclemax@gmail.com>
---
 drivers/pinctrl/pinctrl-mcp23s08.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c
index 78ff7930649d..23af441aa468 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08.c
@@ -622,6 +622,11 @@ int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev,
 	if (ret < 0)
 		return ret;
 
+	/* Also reset all out latches to default values */
+	ret = mcp_write(mcp, MCP_OLAT, 0x0);
+	if (ret < 0)
+		return ret;
+
 	/* verify MCP_IOCON.SEQOP = 0, so sequential reads work,
 	 * and MCP_IOCON.HAEN = 1, so we work with all chips.
 	 */
-- 
2.48.1