From 3ede3f8b4b4b399b0ca41e44959f80d5cf84fc98 Mon Sep 17 00:00:00 2001 From: Mike Looijmans Date: Fri, 14 Mar 2025 16:17:45 +0100 Subject: [PATCH] pinctrl: mcp23s08: Reset all pins to input at probe At startup, the driver just assumes that all registers have their default values. But after a soft reset, the chip will just be in the state it was, and some pins may have been configured as outputs. Any modification of the output register will cause these pins to be driven low, which leads to unexpected/unwanted effects. To prevent this from happening, set the chip's IO configuration register to a known safe mode (all inputs) before toggling any other bits. Signed-off-by: Mike Looijmans Link: https://lore.kernel.org/20250314151803.28903-1-mike.looijmans@topic.nl Signed-off-by: Linus Walleij --- drivers/pinctrl/pinctrl-mcp23s08.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c index 4d1f41488017..c2f4b16f42d2 100644 --- a/drivers/pinctrl/pinctrl-mcp23s08.c +++ b/drivers/pinctrl/pinctrl-mcp23s08.c @@ -636,6 +636,14 @@ int mcp23s08_probe_one(struct mcp23s08 *mcp, struct device *dev, mcp->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW); + /* + * Reset the chip - we don't really know what state it's in, so reset + * all pins to input first to prevent surprises. + */ + ret = mcp_write(mcp, MCP_IODIR, mcp->chip.ngpio == 16 ? 0xFFFF : 0xFF); + 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. */ -- 2.25.1