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Date: Thu, 6 Oct 2022 12:15:06 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Sascha Hauer <s.hauer@...gutronix.de>
Cc: linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>,
Bartosz Golaszewski <brgl@...ev.pl>, kernel@...gutronix.de
Subject: Re: [PATCH v4 1/2] gpio: Add gpio latch driver
On Thu, Oct 06, 2022 at 10:30:30AM +0200, Sascha Hauer wrote:
> 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@...gutronix.de>
> ---
>
> Notes:
> Changes since v3:
> - Introduce delays between GPIO toggles as suggested by Serge Semin
>
> 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 | 220 ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 227 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..a4ab8f1240450
> --- /dev/null
> +++ b/drivers/gpio/gpio-latch.c
> @@ -0,0 +1,220 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * GPIO latch driver
> + *
> + * Copyright (C) 2022 Sascha Hauer <s.hauer@...gutronix.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 <linux/delay.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 int setup_duration_ns;
> + unsigned int clock_duration_ns;
> + 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));
> +
> + ndelay(priv->setup_duration_ns);
> + set(priv->clk_gpios->desc[latch], 1);
> + udelay(priv->clock_duration_ns);
These are supposed to be !n!delay()'s. Aren't they?
> + set(priv->clk_gpios->desc[latch], 0);
> + udelay(priv->clock_duration_ns);
Why do you need the second clock-duration? AFAICS at least from the
TI SNx4LV74A specification the outputs get updated on the positive
edge of the pulse. So the clock-duration value shall contain both
the "CLK pulse duration" and "CLK hold time", which should be enough
for the latches states being perceived by the device.
> +}
> +
> +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;
> + struct device_node *np = pdev->dev.of_node;
> + /*
> + * Some value which is still acceptable to delay in atomic context.
> + * If we need to go higher we might have to switch to usleep_range(),
> + * but that cannot ne used in atomic context and the driver would have
> + * to be adjusted to support that.
> + */
> + unsigned int duration_ns_max = 5000;
I don't see you changing this parameter. So it's better to be a macro.
-Sergey
> +
> + 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);
> + }
> +
> + of_property_read_u32(np, "setup-duration-ns", &priv->setup_duration_ns);
> + if (priv->setup_duration_ns > duration_ns_max) {
> + dev_warn(&pdev->dev, "setup-duration-ns too high, limit to %d\n",
> + duration_ns_max);
> + priv->setup_duration_ns = duration_ns_max;
> + }
> +
> + of_property_read_u32(np, "clock-duration-ns", &priv->clock_duration_ns);
> + if (priv->clock_duration_ns > duration_ns_max) {
> + dev_warn(&pdev->dev, "clock-duration-ns too high, limit to %d\n",
> + duration_ns_max);
> + priv->clock_duration_ns = duration_ns_max;
> + }
> +
> + 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@...gutronix.de>");
> +MODULE_DESCRIPTION("GPIO latch driver");
> --
> 2.30.2
>
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