linux-kernel - [PATCH] pinctrl-mcp23s08: Reset all pins to input at probe

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Message-ID: <20250314151803.28903-1-mike.looijmans@topic.nl>
Date: Fri, 14 Mar 2025 16:17:45 +0100
From: Mike Looijmans <mike.looijmans@...ic.nl>
To: linux-gpio@...r.kernel.org
CC: Mike Looijmans <mike.looijmans@...ic.nl>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org
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 <mike.looijmans@...ic.nl>
---

 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 b96e6368a956..de2147cfe83f 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08.c
@@ -619,6 +619,14 @@ 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.
 	 */
-- 
2.43.0


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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