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    Subject[PATCH v3 1/2] gpio: Add gpio latch driver
    Date
    This driver implements a GPIO multiplexer based on latches connected to
    other GPIOs. A set of data GPIOs is connected to the data input of
    multiple latches. The clock input of each latch is driven by another
    set of GPIOs. With two 8-bit latches 10 GPIOs can be multiplexed into
    16 GPIOs. GPOs might be a better term as in fact the multiplexed pins
    are output only.

    Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
    ---

    Notes:
    Changes since v2:
    - Fix inconsistent licensing
    - document locks
    - use regular bit operations
    - include linux/mod_devicetable.h rather than linux/of_device.h
    - Put spinlock and mutex into a union to make clear that only one of them is used
    - rename __gpio_latch_set to gpio_latch_set_unlocked

    Changes since v1:
    - Use gpiod_set_value_cansleep when the underlying GPIOs might sleep
    - Move MODULE_DEVICE_TABLE near to the end

    drivers/gpio/Kconfig | 6 ++
    drivers/gpio/Makefile | 1 +
    drivers/gpio/gpio-latch.c | 192 ++++++++++++++++++++++++++++++++++++++
    3 files changed, 199 insertions(+)
    create mode 100644 drivers/gpio/gpio-latch.c

    diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
    index 0642f579196f2..e4603810ec910 100644
    --- a/drivers/gpio/Kconfig
    +++ b/drivers/gpio/Kconfig
    @@ -1690,6 +1690,12 @@ config GPIO_AGGREGATOR
    industrial control context, to be operated from userspace using
    the GPIO chardev interface.

    +config GPIO_LATCH
    + tristate "GPIO latch driver"
    + help
    + Say yes here to enable a driver for GPIO multiplexers based on latches
    + connected to other GPIOs.
    +
    config GPIO_MOCKUP
    tristate "GPIO Testing Driver"
    select IRQ_SIM
    diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
    index a0985d30f51bb..310fa08decc69 100644
    --- a/drivers/gpio/Makefile
    +++ b/drivers/gpio/Makefile
    @@ -75,6 +75,7 @@ obj-$(CONFIG_GPIO_IT87) += gpio-it87.o
    obj-$(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_LOGICVC) += gpio-logicvc.o
    obj-$(CONFIG_GPIO_LOONGSON1) += gpio-loongson1.o
    obj-$(CONFIG_GPIO_LOONGSON) += gpio-loongson.o
    diff --git a/drivers/gpio/gpio-latch.c b/drivers/gpio/gpio-latch.c
    new file mode 100644
    index 0000000000000..4134cba1c88a8
    --- /dev/null
    +++ b/drivers/gpio/gpio-latch.c
    @@ -0,0 +1,192 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * GPIO latch driver
    + *
    + * Copyright (C) 2022 Sascha Hauer <s.hauer@pengutronix.de>
    + *
    + * This driver implements a GPIO (or better GPO as there is no input)
    + * multiplexer based on latches like this:
    + *
    + * CLK0 ----------------------. ,--------.
    + * CLK1 -------------------. `--------|> #0 |
    + * | | |
    + * OUT0 ----------------+--|-----------|D0 Q0|-----|<
    + * OUT1 --------------+-|--|-----------|D1 Q1|-----|<
    + * OUT2 ------------+-|-|--|-----------|D2 Q2|-----|<
    + * OUT3 ----------+-|-|-|--|-----------|D3 Q3|-----|<
    + * OUT4 --------+-|-|-|-|--|-----------|D4 Q4|-----|<
    + * OUT5 ------+-|-|-|-|-|--|-----------|D5 Q5|-----|<
    + * OUT6 ----+-|-|-|-|-|-|--|-----------|D6 Q6|-----|<
    + * OUT7 --+-|-|-|-|-|-|-|--|-----------|D7 Q7|-----|<
    + * | | | | | | | | | `--------'
    + * | | | | | | | | |
    + * | | | | | | | | | ,--------.
    + * | | | | | | | | `-----------|> #1 |
    + * | | | | | | | | | |
    + * | | | | | | | `--------------|D0 Q0|-----|<
    + * | | | | | | `----------------|D1 Q1|-----|<
    + * | | | | | `------------------|D2 Q2|-----|<
    + * | | | | `--------------------|D3 Q3|-----|<
    + * | | | `----------------------|D4 Q4|-----|<
    + * | | `------------------------|D5 Q5|-----|<
    + * | `--------------------------|D6 Q6|-----|<
    + * `----------------------------|D7 Q7|-----|<
    + * `--------'
    + *
    + * The above is just an example. The actual number of number of latches and
    + * the number of inputs per latch is derived from the number of GPIOs given
    + * in the corresponding device tree properties.
    + */
    +
    +#include <linux/err.h>
    +#include <linux/gpio/consumer.h>
    +#include <linux/gpio/driver.h>
    +#include <linux/module.h>
    +#include <linux/mod_devicetable.h>
    +#include <linux/platform_device.h>
    +
    +#include "gpiolib.h"
    +
    +struct gpio_latch_priv {
    + struct gpio_chip gc;
    + struct gpio_descs *clk_gpios;
    + struct gpio_descs *latched_gpios;
    + int n_latched_gpios;
    + unsigned long *shadow;
    + /*
    + * Depending on whether any of the underlying GPIOs may sleep we either
    + * use a mutex or a spinlock to protect our shadow map.
    + */
    + union {
    + struct mutex mutex; /* protects @shadow */
    + spinlock_t spinlock; /* protects @shadow */
    + };
    +};
    +
    +static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
    +{
    + return GPIO_LINE_DIRECTION_OUT;
    +}
    +
    +static void gpio_latch_set_unlocked(struct gpio_latch_priv *priv,
    + void (*set)(struct gpio_desc *desc, int value),
    + unsigned int offset, bool val)
    +{
    + int latch = offset / priv->n_latched_gpios;
    + int i;
    +
    + assign_bit(offset, priv->shadow, val);
    +
    + for (i = 0; i < priv->n_latched_gpios; i++)
    + set(priv->latched_gpios->desc[i],
    + test_bit(latch * priv->n_latched_gpios + i, priv->shadow));
    +
    + set(priv->clk_gpios->desc[latch], 1);
    + set(priv->clk_gpios->desc[latch], 0);
    +}
    +
    +static void gpio_latch_set(struct gpio_chip *gc, unsigned int offset, int val)
    +{
    + struct gpio_latch_priv *priv = gpiochip_get_data(gc);
    + unsigned long flags;
    +
    + spin_lock_irqsave(&priv->spinlock, flags);
    +
    + gpio_latch_set_unlocked(priv, gpiod_set_value, offset, val);
    +
    + spin_unlock_irqrestore(&priv->spinlock, flags);
    +}
    +
    +static void gpio_latch_set_can_sleep(struct gpio_chip *gc, unsigned int offset, int val)
    +{
    + struct gpio_latch_priv *priv = gpiochip_get_data(gc);
    +
    + mutex_lock(&priv->mutex);
    +
    + gpio_latch_set_unlocked(priv, gpiod_set_value_cansleep, offset, val);
    +
    + mutex_unlock(&priv->mutex);
    +}
    +
    +static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv, unsigned int n_latches)
    +{
    + int i;
    +
    + for (i = 0; i < n_latches; i++)
    + if (gpiod_cansleep(priv->clk_gpios->desc[i]))
    + return true;
    +
    + for (i = 0; i < priv->n_latched_gpios; i++)
    + if (gpiod_cansleep(priv->latched_gpios->desc[i]))
    + return true;
    +
    + return false;
    +}
    +
    +static int gpio_latch_probe(struct platform_device *pdev)
    +{
    + struct gpio_latch_priv *priv;
    + unsigned int n_latches;
    +
    + priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
    + if (!priv)
    + return -ENOMEM;
    +
    + priv->clk_gpios = devm_gpiod_get_array(&pdev->dev, "clk", GPIOD_OUT_LOW);
    + if (IS_ERR(priv->clk_gpios))
    + return PTR_ERR(priv->clk_gpios);
    +
    + priv->latched_gpios = devm_gpiod_get_array(&pdev->dev, "latched", GPIOD_OUT_LOW);
    + if (IS_ERR(priv->latched_gpios))
    + return PTR_ERR(priv->latched_gpios);
    +
    + n_latches = priv->clk_gpios->ndescs;
    + priv->n_latched_gpios = priv->latched_gpios->ndescs;
    +
    + priv->shadow = devm_bitmap_zalloc(&pdev->dev, n_latches * priv->n_latched_gpios,
    + GFP_KERNEL);
    + if (!priv->shadow)
    + return -ENOMEM;
    +
    + if (gpio_latch_can_sleep(priv, n_latches)) {
    + priv->gc.can_sleep = true;
    + priv->gc.set = gpio_latch_set_can_sleep;
    + mutex_init(&priv->mutex);
    + } else {
    + priv->gc.can_sleep = false;
    + priv->gc.set = gpio_latch_set;
    + spin_lock_init(&priv->spinlock);
    + }
    +
    + priv->gc.get_direction = gpio_latch_get_direction;
    + priv->gc.ngpio = n_latches * priv->n_latched_gpios;
    + priv->gc.owner = THIS_MODULE;
    + priv->gc.base = -1;
    + priv->gc.parent = &pdev->dev;
    +
    + platform_set_drvdata(pdev, priv);
    +
    + return devm_gpiochip_add_data(&pdev->dev, &priv->gc, priv);
    +}
    +
    +static const struct of_device_id gpio_latch_ids[] = {
    + {
    + .compatible = "gpio-latch",
    + }, {
    + /* sentinel */
    + }
    +};
    +MODULE_DEVICE_TABLE(of, gpio_latch_ids);
    +
    +static struct platform_driver gpio_latch_driver = {
    + .driver = {
    + .name = "gpio-latch",
    + .of_match_table = gpio_latch_ids,
    + },
    + .probe = gpio_latch_probe,
    +};
    +module_platform_driver(gpio_latch_driver);
    +
    +MODULE_LICENSE("GPL v2");
    +MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");
    +MODULE_DESCRIPTION("GPIO latch driver");
    --
    2.30.2
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      Last update: 2022-09-14 09:14    [W:25.315 / U:0.012 seconds]
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