[PATCH v2] mux: gpio-mux: add support for 4:1 2-channels mux

[Andrea Tomassetti]

Some gpio multiplexers, like TMUX1209, offer differential 4:1
or dual 4:1 single-ended channels. No binding changes are needed
because the DT binding already supports #mux-control-cells
with values 0 and 1. So, similarly to what was already done by the
adg792a driver, the gpio-mux driver has to take into account
the #mux-control-cells property and allocate as many controllers as
advised by it.

As an example, in the DTS you can now define:

	tmux1209: mux-controller {
		compatible = "gpio-mux";
		#mux-control-cells = <1>;

		mux-gpios = <&gpio_expander 01 GPIO_ACTIVE_HIGH>,
			    <&gpio_expander 02 GPIO_ACTIVE_HIGH>;
	};

And use it like this:

	adcmux30: adcmux30 {
		compatible = "io-channel-mux";
		io-channels = <&adc1 4>;
		io-channel-names = "parent";
		#io-channel-cells = <1>;
		mux-controls = <&tmux1209 0>;

		channels = "S1A", "S2A", "S3A", "S4A";
	};

	adcmux31: adcmux31 {
		compatible = "io-channel-mux";
		io-channels = <&adc1 5>;
		io-channel-names = "parent";
		#io-channel-cells = <1>;
		mux-controls = <&tmux1209 1>;

		channels = "S1B", "S2B", "S3B", "S4B";
	};

Signed-off-by: Andrea Tomassetti <andrea.tomassetti@xxxxxxxxxxx>
Reviewed-by: Linus Walleij <linusw@xxxxxxxxxx>
---
v2: Address feedback from Linus Walleij
  - reword commit message by making clear that patching the binding
    is not needed
  - make clear from error message that binding only allows 0 or 1
  - fix two other locations where `mux` was accessed

 drivers/mux/gpio.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/mux/gpio.c b/drivers/mux/gpio.c
index 4cc3202c58f3..ab3ed5247d2c 100644
--- a/drivers/mux/gpio.c
+++ b/drivers/mux/gpio.c
@@ -52,12 +52,23 @@ static int mux_gpio_probe(struct platform_device *pdev)
 	int pins;
 	s32 idle_state;
 	int ret;
+	u32 cells;
+	int i;

 	pins = gpiod_count(dev, "mux");
 	if (pins < 0)
 		return pins;

-	mux_chip = devm_mux_chip_alloc(dev, 1, sizeof(*mux_gpio));
+	ret = device_property_read_u32(dev, "#mux-control-cells", &cells);
+	if (ret < 0)
+		cells = 0;
+
+	if (cells >= 2) {
+		dev_err(dev, "invalid control-cells %u, must be 0 or 1\n", cells);
+		return -EINVAL;
+	}
+
+	mux_chip = devm_mux_chip_alloc(dev, cells + 1, sizeof(*mux_gpio));
 	if (IS_ERR(mux_chip))
 		return PTR_ERR(mux_chip);

@@ -69,7 +80,9 @@ static int mux_gpio_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(mux_gpio->gpios),
 				     "failed to get gpios\n");
 	WARN_ON(pins != mux_gpio->gpios->ndescs);
-	mux_chip->mux->states = BIT(pins);
+
+	for (i = 0; i < mux_chip->controllers; ++i)
+		mux_chip->mux[i].states = BIT(pins);

 	ret = device_property_read_u32(dev, "idle-state", (u32 *)&idle_state);
 	if (ret >= 0 && idle_state != MUX_IDLE_AS_IS) {
@@ -78,7 +91,8 @@ static int mux_gpio_probe(struct platform_device *pdev)
 			return -EINVAL;
 		}

-		mux_chip->mux->idle_state = idle_state;
+		for (i = 0; i < mux_chip->controllers; ++i)
+			mux_chip->mux[i].idle_state = idle_state;
 	}

 	ret = devm_regulator_get_enable_optional(dev, "mux");
@@ -89,8 +103,8 @@ static int mux_gpio_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;

-	dev_info(dev, "%u-way mux-controller registered\n",
-		 mux_chip->mux->states);
+	dev_info(dev, "%u-way mux-controller registered, %u controllers\n",
+		 mux_chip->mux->states, mux_chip->controllers);

 	return 0;
 }

base-commit: 74fe02ce122a6103f207d29fafc8b3a53de6abaf
--
2.51.2