linux-kernel - [PATCH v3 2/4] mux: gpio-mux: add support for enable GPIO

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Message-ID: <20260115121943.23715-3-antoniu.miclaus@analog.com>
Date: Thu, 15 Jan 2026 14:18:20 +0200
From: Antoniu Miclaus <antoniu.miclaus@...log.com>
To: Peter Rosin <peda@...ntia.se>, Rob Herring <robh@...nel.org>,
        Krzysztof
 Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Antoniu
 Miclaus <antoniu.miclaus@...log.com>,
        Srinivas Kandagatla <srini@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski
	<bartosz.golaszewski@...aro.org>,
        David Lechner <dlechner@...libre.com>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 2/4] mux: gpio-mux: add support for enable GPIO

Add support for an optional enable GPIO to the gpio-mux driver. This
allows the mux to be disabled before changing address lines and
re-enabled after, preventing glitches that could briefly activate
unintended channels during transitions.

The enable GPIO is optional and the driver maintains backward
compatibility with existing gpio-mux users.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
---
changes in v3:
 * new patch - extend gpio-mux instead of standalone driver approach
---
 drivers/mux/gpio.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/drivers/mux/gpio.c b/drivers/mux/gpio.c
index 4cc3202c58f3..93487483e81f 100644
--- a/drivers/mux/gpio.c
+++ b/drivers/mux/gpio.c
@@ -19,6 +19,7 @@
 
 struct mux_gpio {
 	struct gpio_descs *gpios;
+	struct gpio_desc *enable;
 };
 
 static int mux_gpio_set(struct mux_control *mux, int state)
@@ -27,10 +28,28 @@ static int mux_gpio_set(struct mux_control *mux, int state)
 	DECLARE_BITMAP(values, BITS_PER_TYPE(state));
 	u32 value = state;
 
+	if (state == MUX_IDLE_DISCONNECT) {
+		if (mux_gpio->enable)
+			gpiod_set_value_cansleep(mux_gpio->enable, 0);
+		return 0;
+	}
+
+	if (mux_gpio->enable) {
+		/*
+		 * Disable the mux before changing address lines to prevent
+		 * glitches. Changing address while enabled could briefly
+		 * activate an unintended channel during the transition.
+		 */
+		gpiod_set_value_cansleep(mux_gpio->enable, 0);
+	}
+
 	bitmap_from_arr32(values, &value, BITS_PER_TYPE(value));
 
 	gpiod_multi_set_value_cansleep(mux_gpio->gpios, values);
 
+	if (mux_gpio->enable)
+		gpiod_set_value_cansleep(mux_gpio->enable, 1);
+
 	return 0;
 }
 
@@ -71,9 +90,20 @@ static int mux_gpio_probe(struct platform_device *pdev)
 	WARN_ON(pins != mux_gpio->gpios->ndescs);
 	mux_chip->mux->states = BIT(pins);
 
+	mux_gpio->enable = devm_gpiod_get_optional(dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(mux_gpio->enable))
+		return dev_err_probe(dev, PTR_ERR(mux_gpio->enable),
+				     "failed to get enable gpio\n");
+
 	ret = device_property_read_u32(dev, "idle-state", (u32 *)&idle_state);
 	if (ret >= 0 && idle_state != MUX_IDLE_AS_IS) {
-		if (idle_state < 0 || idle_state >= mux_chip->mux->states) {
+		if (idle_state == MUX_IDLE_DISCONNECT) {
+			if (!mux_gpio->enable) {
+				dev_err(dev,
+					"invalid idle-state (MUX_IDLE_DISCONNECT requires enable-gpios)\n");
+				return -EINVAL;
+			}
+		} else if (idle_state < 0 || idle_state >= mux_chip->mux->states) {
 			dev_err(dev, "invalid idle-state %u\n", idle_state);
 			return -EINVAL;
 		}
-- 
2.43.0