Re: [PATCH v3 1/2] gpio: Add gpio latch driver
From: Serge Semin <hidden>
Date: 2022-09-14 14:04:38
Also in:
linux-gpio, lkml
On Wed, Sep 14, 2022 at 09:13:05AM +0200, Sascha Hauer wrote:
quoted hunk ↗ jump to hunk
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.cdiff --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_SIMdiff --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.odiff --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));
-> duration?
+ + set(priv->clk_gpios->desc[latch], 1);
-> duration?
+ set(priv->clk_gpios->desc[latch], 0);
I am pretty much sure there must be some duration between the actions above *. See for instance the tw and (tsu + th) timing requirements in the next edge-triggered flip-flops: https://www.ti.com/lit/ds/symlink/sn74lv74a.pdf?ts=1663163389954&ref_url=https%253A%252F%252Fwww.google.com%252F The durations are normally small (ns or a bit smaller) but still need to be added anyway. Note since the durations are device-specific an additional DT-property array with durations should be added too. * already faced weird problems in this regard. -Sergey
+}
+
+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 [off-list ref]");
+MODULE_DESCRIPTION("GPIO latch driver");
--
2.30.2