6.15-stable review patch. If anyone has any objections, please let me know.
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From: Mike Looijmans mike.looijmans@topic.nl
[ Upstream commit 3ede3f8b4b4b399b0ca41e44959f80d5cf84fc98 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 4d1f41488017e..c2f4b16f42d20 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. */