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pinctrl: mcp23s08: Reset all pins to input at probe

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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 <mike.looijmans@topic.nl>
Link: https://lore.kernel.org/20250314151803.28903-1-mike.looijmans@topic.nl
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Mike Looijmans 2025-03-14 16:17:45 +01:00 • committed by Linus Walleij
parent a63cafe241
commit 3ede3f8b4b
1 changed files with 8 additions and 0 deletions
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8
drivers/pinctrl/pinctrl-mcp23s08.c
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@ -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.
*/