gpio: add gpio-line-mux driver

Add a new driver which provides a 1-to-many mapping for a single real
GPIO using a multiplexer. Each virtual GPIO corresponds to a multiplexer
state which, if set for the multiplexer, connects the real GPIO to the
corresponding virtual GPIO.

This can help in various usecases. One practical case is the special
hardware design of the Realtek-based XS1930-10 switch from Zyxel. It
features two SFP+ ports/cages whose signals are wired directly to the
switch SoC. Although Realtek SoCs are short on GPIOs, there are usually
enough the fit the SFP signals without any hacks.

However, Zyxel did some weird design and connected RX_LOS, MOD_ABS and
TX_FAULT of one SFP cage onto a single GPIO line controlled by a
multiplexer (the same for the other SFP cage). The single multiplexer
controls the lines for both SFP and depending on the state, the
designated 'signal GPIO lines' are connected to one of the three SFP
signals.

Because the SFP core/driver doesn't support multiplexer but needs single
GPIOs for each of the signals, this driver fills the gap between both.
It registers a gpio_chip, provides multiple virtual GPIOs and sets the
backing multiplexer accordingly.

Due to several practical issues, this is input-only and doesn't support
IRQs.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Reviewed-by: Thomas Richard <thomas.richard@bootlin.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20251227180134.1262138-3-jelonek.jonas@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

diff --git a/MAINTAINERS b/MAINTAINERS
index 5b11839cba9de1e9e43f63787578edd8c429ca39..8056ef0ffbf02d6a2cc3214d98258ad7b29e47ff 100644 (file)
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10774,6 +10774,12 @@ S:     Maintained
 F:     Documentation/devicetree/bindings/leds/irled/gpio-ir-tx.yaml
 F:     drivers/media/rc/gpio-ir-tx.c
 
+GPIO LINE MUX
+M:     Jonas Jelonek <jelonek.jonas@gmail.com>
+S:     Maintained
+F:     Documentation/devicetree/bindings/gpio/gpio-line-mux.yaml
+F:     drivers/gpio/gpio-line-mux.c
+
 GPIO MOCKUP DRIVER
 M:     Bamvor Jian Zhang <bamv2005@gmail.com>
 L:     linux-gpio@vger.kernel.org

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index c33f9305ab97734a0be126789af5360bdcde13b8..2efa58f1078122ba347e15ce87234a5c387ad6b4 100644 (file)
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1994,6 +1994,15 @@ config GPIO_LATCH
          Say yes here to enable a driver for GPIO multiplexers based on latches
          connected to other GPIOs.
 
+config GPIO_LINE_MUX
+       tristate "GPIO line mux driver"
+       depends on OF_GPIO
+       select MULTIPLEXER
+       help
+         Say Y here to support the GPIO line mux, which can provide virtual
+         GPIOs backed by a shared real GPIO and a multiplexer in a 1-to-many
+         fashion.
+
 config GPIO_MOCKUP
        tristate "GPIO Testing Driver (DEPRECATED)"
        select IRQ_SIM

diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 2421a8fd3733e0b06c2581262aaa9cd629f66c7d..36fa7c52d24087da0edb6b8c298eb8f940f07e27 100644 (file)
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -90,6 +90,7 @@ obj-$(CONFIG_GPIO_IXP4XX)             += gpio-ixp4xx.o
 obj-$(CONFIG_GPIO_JANZ_TTL)            += gpio-janz-ttl.o
 obj-$(CONFIG_GPIO_KEMPLD)              += gpio-kempld.o
 obj-$(CONFIG_GPIO_LATCH)               += gpio-latch.o
+obj-$(CONFIG_GPIO_LINE_MUX)            += gpio-line-mux.o
 obj-$(CONFIG_GPIO_LJCA)                += gpio-ljca.o
 obj-$(CONFIG_GPIO_LOGICVC)             += gpio-logicvc.o
 obj-$(CONFIG_GPIO_LOONGSON1)           += gpio-loongson1.o

diff --git a/drivers/gpio/gpio-line-mux.c b/drivers/gpio/gpio-line-mux.c
new file mode 100644 (file)
index 0000000..a4f3843
--- /dev/null
+++ b/drivers/gpio/gpio-line-mux.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * GPIO line mux which acts as virtual gpiochip and provides a 1-to-many
+ * mapping between virtual GPIOs and a real GPIO + multiplexer.
+ *
+ * Copyright (c) 2025 Jonas Jelonek <jelonek.jonas@gmail.com>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/gpio/driver.h>
+#include <linux/mod_devicetable.h>
+#include <linux/mutex.h>
+#include <linux/mux/consumer.h>
+#include <linux/platform_device.h>
+
+#define MUX_SELECT_DELAY_US    100
+
+struct gpio_lmux {
+       struct gpio_chip gc;
+       struct mux_control *mux;
+       struct gpio_desc *muxed_gpio;
+
+       u32 num_gpio_mux_states;
+       unsigned int gpio_mux_states[] __counted_by(num_gpio_mux_states);
+};
+
+static int gpio_lmux_gpio_get(struct gpio_chip *gc, unsigned int offset)
+{
+       struct gpio_lmux *glm = gpiochip_get_data(gc);
+       int ret;
+
+       if (offset > gc->ngpio)
+               return -EINVAL;
+
+       ret = mux_control_select_delay(glm->mux, glm->gpio_mux_states[offset],
+                                      MUX_SELECT_DELAY_US);
+       if (ret < 0)
+               return ret;
+
+       ret = gpiod_get_raw_value_cansleep(glm->muxed_gpio);
+       mux_control_deselect(glm->mux);
+       return ret;
+}
+
+static int gpio_lmux_gpio_set(struct gpio_chip *gc, unsigned int offset,
+                             int value)
+{
+       return -EOPNOTSUPP;
+}
+
+static int gpio_lmux_gpio_get_direction(struct gpio_chip *gc,
+                                       unsigned int offset)
+{
+       return GPIO_LINE_DIRECTION_IN;
+}
+
+static int gpio_lmux_probe(struct platform_device *pdev)
+{
+       struct device *dev = &pdev->dev;
+       struct gpio_lmux *glm;
+       unsigned int ngpio;
+       size_t size;
+       int ret;
+
+       ngpio = device_property_count_u32(dev, "gpio-line-mux-states");
+       if (!ngpio)
+               return -EINVAL;
+
+       size = struct_size(glm, gpio_mux_states, ngpio);
+       glm = devm_kzalloc(dev, size, GFP_KERNEL);
+       if (!glm)
+               return -ENOMEM;
+
+       glm->gc.base = -1;
+       glm->gc.can_sleep = true;
+       glm->gc.fwnode = dev_fwnode(dev);
+       glm->gc.label = dev_name(dev);
+       glm->gc.ngpio = ngpio;
+       glm->gc.owner = THIS_MODULE;
+       glm->gc.parent = dev;
+
+       glm->gc.get = gpio_lmux_gpio_get;
+       glm->gc.set = gpio_lmux_gpio_set;
+       glm->gc.get_direction = gpio_lmux_gpio_get_direction;
+
+       glm->mux = devm_mux_control_get(dev, NULL);
+       if (IS_ERR(glm->mux))
+               return dev_err_probe(dev, PTR_ERR(glm->mux),
+                                    "could not get mux controller\n");
+
+       glm->muxed_gpio = devm_gpiod_get(dev, "muxed", GPIOD_IN);
+       if (IS_ERR(glm->muxed_gpio))
+               return dev_err_probe(dev, PTR_ERR(glm->muxed_gpio),
+                                    "could not get muxed-gpio\n");
+
+       glm->num_gpio_mux_states = ngpio;
+       ret = device_property_read_u32_array(dev, "gpio-line-mux-states",
+                                            &glm->gpio_mux_states[0], ngpio);
+       if (ret)
+               return dev_err_probe(dev, ret, "could not get mux states\n");
+
+       ret = devm_gpiochip_add_data(dev, &glm->gc, glm);
+       if (ret)
+               return dev_err_probe(dev, ret, "failed to add gpiochip\n");
+
+       return 0;
+}
+
+static const struct of_device_id gpio_lmux_of_match[] = {
+       { .compatible = "gpio-line-mux" },
+       { }
+};
+MODULE_DEVICE_TABLE(of, gpio_lmux_of_match);
+
+static struct platform_driver gpio_lmux_driver = {
+       .driver = {
+               .name = "gpio-line-mux",
+               .of_match_table = gpio_lmux_of_match,
+       },
+       .probe = gpio_lmux_probe,
+};
+module_platform_driver(gpio_lmux_driver);
+
+MODULE_AUTHOR("Jonas Jelonek <jelonek.jonas@gmail.com>");
+MODULE_DESCRIPTION("GPIO line mux driver");
+MODULE_LICENSE("GPL");