Commit 3ede3f8b authored by Mike Looijmans's avatar Mike Looijmans Committed by Linus Walleij
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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: default avatarMike Looijmans <mike.looijmans@topic.nl>
Link: https://lore.kernel.org/20250314151803.28903-1-mike.looijmans@topic.nl


Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent a63cafe2

drivers/pinctrl/pinctrl-mcp23s08.c

+8 −0
Original line number Diff line number Diff line
@@ -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.

	 */