[PATCH v2 0/2] gpio: Add gpio-latch driver

[PATCH v2 0/2] gpio: Add gpio-latch driver

[Sascha Hauer]

This adds a gpio-driver which multiplexes existing GPIOs using latches.
Uwe asked [1] if that would be accectable as a new gpio driver, and here
is the result. For a better description what this is all about have a
look at the drawings in the patches.

Sascha

[1] https://lore.kernel.org/all/CACRpkdaBO=JzokGUF6uXZc7ASVD7LjqBxTLGwX-FShM=A9gw9A@mail.gmail.com/t/

Changes since v1:
    - Use gpiod_set_value_cansleep when the underlying GPIOs might sleep
    - Move MODULE_DEVICE_TABLE near to the end
    - Add license to binding file
    - remove trailing whitespaces


Sascha Hauer (2):
  gpio: Add gpio latch driver
  dt-bindings: gpio: Add gpio-latch binding document

 .../devicetree/bindings/gpio/gpio-latch.yaml  |  84 ++++++++
 drivers/gpio/Kconfig                          |   6 +
 drivers/gpio/Makefile                         |   1 +
 drivers/gpio/gpio-latch.c                     | 190 ++++++++++++++++++
 4 files changed, 281 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/gpio/gpio-latch.yaml
 create mode 100644 drivers/gpio/gpio-latch.c

-- 
2.30.2

[PATCH v2 1/2] gpio: Add gpio latch driver

[Sascha Hauer]

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>
---
 drivers/gpio/Kconfig      |   6 ++
 drivers/gpio/Makefile     |   1 +
 drivers/gpio/gpio-latch.c | 190 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 197 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..4068ed4066272
--- /dev/null
+++ b/drivers/gpio/gpio-latch.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * 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/module.h>
+#include <linux/of_device.h>
+#include <linux/gpio/driver.h>
+#include <linux/platform_device.h>
+#include <linux/gpio/consumer.h>
+
+#include "gpiolib.h"
+
+struct gpio_latch_priv {
+	struct gpio_chip gc;
+	struct gpio_descs *clk_gpios;
+	struct gpio_descs *data_gpios;
+	spinlock_t lock;
+	int n_ports;
+	int n_pins;
+	unsigned int *shadow;
+	struct mutex mutex;
+	spinlock_t spinlock;
+};
+
+static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
+{
+	return GPIO_LINE_DIRECTION_OUT;
+}
+
+static void __gpio_latch_set(struct gpio_latch_priv *priv,
+			     void (* set)(struct gpio_desc *desc, int value),
+			     unsigned int offset, int val)
+{
+	int latch = offset / priv->n_pins;
+	int i;
+
+	if (val)
+		priv->shadow[latch] |= BIT(offset % priv->n_pins);
+	else
+		priv->shadow[latch] &= ~BIT(offset % priv->n_pins);
+
+	for (i = 0; i < priv->n_pins; i++)
+		set(priv->data_gpios->desc[i], priv->shadow[latch] & BIT(i));
+
+	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(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(priv, gpiod_set_value_cansleep, offset, val);
+
+	mutex_unlock(&priv->mutex);
+}
+
+static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv)
+{
+	int i;
+
+	for (i = 0; i < priv->n_ports; i++)
+		if (gpiod_cansleep(priv->clk_gpios->desc[i]))
+			return true;
+
+	for (i = 0; i < priv->n_pins; i++)
+		if (gpiod_cansleep(priv->data_gpios->desc[i]))
+			return true;
+
+	return false;
+}
+
+static int gpio_latch_probe(struct platform_device *pdev)
+{
+	struct gpio_latch_priv *priv;
+
+	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->data_gpios = devm_gpiod_get_array(&pdev->dev, "data", GPIOD_OUT_LOW);
+	if (IS_ERR(priv->data_gpios))
+		return PTR_ERR(priv->data_gpios);
+
+	priv->n_ports = priv->clk_gpios->ndescs;
+	priv->n_pins = priv->data_gpios->ndescs;
+
+	priv->shadow = devm_kcalloc(&pdev->dev, priv->n_ports, sizeof(*priv->shadow),
+				    GFP_KERNEL);
+	if (!priv->shadow)
+		return -ENOMEM;
+
+	if (gpio_latch_can_sleep(priv)) {
+		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 = priv->n_ports * priv->n_pins;
+	priv->gc.owner = THIS_MODULE;
+	priv->gc.base = -1;
+	priv->gc.parent = &pdev->dev;
+	priv->gc.of_node = pdev->dev.of_node;
+
+	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

[PATCH v2 2/2] dt-bindings: gpio: Add gpio-latch binding document

[Sascha Hauer]

This adds a binding for a GPIO multiplexer driver based on latches
connected to other GPIOs.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 .../devicetree/bindings/gpio/gpio-latch.yaml  | 84 +++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/gpio/gpio-latch.yaml

diff --git a/Documentation/devicetree/bindings/gpio/gpio-latch.yaml b/Documentation/devicetree/bindings/gpio/gpio-latch.yaml
new file mode 100644
index 0000000000000..7aa513c10df1a
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/gpio-latch.yaml
@@ -0,0 +1,84 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/gpio-latch.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: GPIO latch controller
+
+maintainers:
+  - Sascha Hauer <s.hauer@pengutronix.de>
+
+description: |
+  This binding describes a GPIO multiplexer based on latches connected to
+  other GPIOs, 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 number of clk-gpios and data-gpios is not fixed. The actual number of
+  GPIOs used for clk and data are taken from the corresponding array lengths.
+
+properties:
+  compatible:
+    const: gpio-latch
+  "#gpio-cells":
+    const: 2
+
+  clk-gpios:
+    description: Array of GPIOs to be used to clock a latch
+
+  data-gpios:
+    description: Array of GPIOs to be used as data GPIOs
+
+  gpio-controller: true
+
+  gpio-line-names: true
+
+required:
+  - compatible
+  - "#gpio-cells"
+  - gpio-controller
+  - clk-gpios
+  - data-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    gpio-latch {
+        #gpio-cells = <2>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&pinctrl_di_do_leds>;
+        compatible = "gpio-latch";
+        gpio-controller;
+
+        clk-gpios = <&gpio3 7 0>, <&gpio3 8 0>;
+        data-gpios = <&gpio3 21 0>, <&gpio3 22 0>,
+                     <&gpio3 23 0>, <&gpio3 24 0>,
+                     <&gpio3 25 0>, <&gpio3 26 0>,
+                     <&gpio3 27 0>, <&gpio3 28 0>;
+    };
-- 
2.30.2

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Marco Felsch]

Hi Sascha,

On 22-08-31, 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@pengutronix.de>

apart the one minor nit (see end) feel free to add my

Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>

> ---
>  drivers/gpio/Kconfig      |   6 ++
>  drivers/gpio/Makefile     |   1 +
>  drivers/gpio/gpio-latch.c | 190 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 197 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..4068ed4066272
> --- /dev/null
> +++ b/drivers/gpio/gpio-latch.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * 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/module.h>
> +#include <linux/of_device.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/platform_device.h>
> +#include <linux/gpio/consumer.h>
> +
> +#include "gpiolib.h"
> +
> +struct gpio_latch_priv {
> +	struct gpio_chip gc;
> +	struct gpio_descs *clk_gpios;
> +	struct gpio_descs *data_gpios;
> +	spinlock_t lock;
> +	int n_ports;
> +	int n_pins;
> +	unsigned int *shadow;
> +	struct mutex mutex;
> +	spinlock_t spinlock;
> +};
> +
> +static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
> +{
> +	return GPIO_LINE_DIRECTION_OUT;
> +}
> +
> +static void __gpio_latch_set(struct gpio_latch_priv *priv,
> +			     void (* set)(struct gpio_desc *desc, int value),
> +			     unsigned int offset, int val)
> +{
> +	int latch = offset / priv->n_pins;
> +	int i;
> +
> +	if (val)
> +		priv->shadow[latch] |= BIT(offset % priv->n_pins);
> +	else
> +		priv->shadow[latch] &= ~BIT(offset % priv->n_pins);
> +
> +	for (i = 0; i < priv->n_pins; i++)
> +		set(priv->data_gpios->desc[i], priv->shadow[latch] & BIT(i));
> +
> +	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(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(priv, gpiod_set_value_cansleep, offset, val);
> +
> +	mutex_unlock(&priv->mutex);
> +}
> +
> +static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv)
> +{
> +	int i;
> +
> +	for (i = 0; i < priv->n_ports; i++)
> +		if (gpiod_cansleep(priv->clk_gpios->desc[i]))
> +			return true;
> +
> +	for (i = 0; i < priv->n_pins; i++)
> +		if (gpiod_cansleep(priv->data_gpios->desc[i]))
> +			return true;
> +
> +	return false;
> +}
> +
> +static int gpio_latch_probe(struct platform_device *pdev)
> +{
> +	struct gpio_latch_priv *priv;
> +
> +	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->data_gpios = devm_gpiod_get_array(&pdev->dev, "data", GPIOD_OUT_LOW);
> +	if (IS_ERR(priv->data_gpios))
> +		return PTR_ERR(priv->data_gpios);
> +
> +	priv->n_ports = priv->clk_gpios->ndescs;
> +	priv->n_pins = priv->data_gpios->ndescs;
> +
> +	priv->shadow = devm_kcalloc(&pdev->dev, priv->n_ports, sizeof(*priv->shadow),
> +				    GFP_KERNEL);
> +	if (!priv->shadow)
> +		return -ENOMEM;
> +
> +	if (gpio_latch_can_sleep(priv)) {
> +		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 = priv->n_ports * priv->n_pins;
> +	priv->gc.owner = THIS_MODULE;
> +	priv->gc.base = -1;
> +	priv->gc.parent = &pdev->dev;
> +	priv->gc.of_node = pdev->dev.of_node;
> +
> +	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");

checkpatch.pl should complain about this since it it now GPL, see commit
bf7fbeeae6db. Sorry for not spotted that earlier.

Regards,
  Marco

> +MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");
> +MODULE_DESCRIPTION("GPIO latch driver");
> -- 
> 2.30.2

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Sascha Hauer]

On Wed, Aug 31, 2022 at 10:01:09AM +0200, Marco Felsch wrote:
> Hi Sascha,
> 
> On 22-08-31, 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@pengutronix.de>
> 
> apart the one minor nit (see end) feel free to add my
> 
> Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
> 
> > +// SPDX-License-Identifier: GPL-2.0-or-later

[snip]

> > +MODULE_LICENSE("GPL v2");
> 
> checkpatch.pl should complain about this since it it now GPL, see commit
> bf7fbeeae6db. Sorry for not spotted that earlier.

Just checked, checkpatch doesn't complain. Will fix in v3

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Bartosz Golaszewski]

On Wed, Aug 31, 2022 at 7:58 AM Sascha Hauer <s.hauer@pengutronix.de> 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@pengutronix.de>
> ---
>  drivers/gpio/Kconfig      |   6 ++
>  drivers/gpio/Makefile     |   1 +
>  drivers/gpio/gpio-latch.c | 190 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 197 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..4068ed4066272
> --- /dev/null
> +++ b/drivers/gpio/gpio-latch.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * 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/module.h>
> +#include <linux/of_device.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/platform_device.h>
> +#include <linux/gpio/consumer.h>
> +
> +#include "gpiolib.h"
> +
> +struct gpio_latch_priv {
> +       struct gpio_chip gc;
> +       struct gpio_descs *clk_gpios;
> +       struct gpio_descs *data_gpios;
> +       spinlock_t lock;
> +       int n_ports;
> +       int n_pins;
> +       unsigned int *shadow;
> +       struct mutex mutex;
> +       spinlock_t spinlock;
> +};
> +
> +static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
> +{
> +       return GPIO_LINE_DIRECTION_OUT;
> +}
> +
> +static void __gpio_latch_set(struct gpio_latch_priv *priv,

I would love to see that renamed to gpio_latch_set_unlocked(). Other
than that, looks good to me.

Bart

> +                            void (* set)(struct gpio_desc *desc, int value),
> +                            unsigned int offset, int val)
> +{
> +       int latch = offset / priv->n_pins;
> +       int i;
> +
> +       if (val)
> +               priv->shadow[latch] |= BIT(offset % priv->n_pins);
> +       else
> +               priv->shadow[latch] &= ~BIT(offset % priv->n_pins);
> +
> +       for (i = 0; i < priv->n_pins; i++)
> +               set(priv->data_gpios->desc[i], priv->shadow[latch] & BIT(i));
> +
> +       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(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(priv, gpiod_set_value_cansleep, offset, val);
> +
> +       mutex_unlock(&priv->mutex);
> +}
> +
> +static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv)
> +{
> +       int i;
> +
> +       for (i = 0; i < priv->n_ports; i++)
> +               if (gpiod_cansleep(priv->clk_gpios->desc[i]))
> +                       return true;
> +
> +       for (i = 0; i < priv->n_pins; i++)
> +               if (gpiod_cansleep(priv->data_gpios->desc[i]))
> +                       return true;
> +
> +       return false;
> +}
> +
> +static int gpio_latch_probe(struct platform_device *pdev)
> +{
> +       struct gpio_latch_priv *priv;
> +
> +       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->data_gpios = devm_gpiod_get_array(&pdev->dev, "data", GPIOD_OUT_LOW);
> +       if (IS_ERR(priv->data_gpios))
> +               return PTR_ERR(priv->data_gpios);
> +
> +       priv->n_ports = priv->clk_gpios->ndescs;
> +       priv->n_pins = priv->data_gpios->ndescs;
> +
> +       priv->shadow = devm_kcalloc(&pdev->dev, priv->n_ports, sizeof(*priv->shadow),
> +                                   GFP_KERNEL);
> +       if (!priv->shadow)
> +               return -ENOMEM;
> +
> +       if (gpio_latch_can_sleep(priv)) {
> +               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 = priv->n_ports * priv->n_pins;
> +       priv->gc.owner = THIS_MODULE;
> +       priv->gc.base = -1;
> +       priv->gc.parent = &pdev->dev;
> +       priv->gc.of_node = pdev->dev.of_node;
> +
> +       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
>

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Andy Shevchenko]

On Wed, Aug 31, 2022 at 9:02 AM Sascha Hauer <s.hauer@pengutronix.de> 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.

I'm still unsure it shouldn't be a part of the (not yet in upstream)
driver that I have mentioned before. But let's leave this apart right
now.

...

> +#include <linux/err.h>
> +#include <linux/module.h>

> +#include <linux/of_device.h>

Why?
It seems you misplaced it instead of mod_devicetable.h.

> +#include <linux/gpio/driver.h>
> +#include <linux/platform_device.h>
> +#include <linux/gpio/consumer.h>

Keep above sorted?

...

> +       struct mutex mutex;
> +       spinlock_t spinlock;

Checkpatch usually complains if locks are not commented. Looking at
the below code, why it's not an (anonymous) union?

...

> +       if (val)
> +               priv->shadow[latch] |= BIT(offset % priv->n_pins);
> +       else
> +               priv->shadow[latch] &= ~BIT(offset % priv->n_pins);

I believe shadow should be defined as unsigned long * and hence normal
bit operations can be applied. For example here is assign_bit().

...

> +       priv->shadow = devm_kcalloc(&pdev->dev, priv->n_ports, sizeof(*priv->shadow),
> +                                   GFP_KERNEL);

bitmap_zalloc()

> +       if (!priv->shadow)
> +               return -ENOMEM;

...

> +       priv->gc.parent = &pdev->dev;

> +       priv->gc.of_node = pdev->dev.of_node;

Redundant as repeating parent above.

...

> +static const struct of_device_id gpio_latch_ids[] = {
> +       {
> +               .compatible     = "gpio-latch",
> +       }, {
> +               /* sentinel */
> +       }

You may compress this to the 2 LoCs.

> +};

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[kernel test robot]

Hi Sascha,

I love your patch! Yet something to improve:

[auto build test ERROR on brgl/gpio/for-next]
[also build test ERROR on linus/master v6.0-rc3 next-20220830]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Sascha-Hauer/gpio-Add-gpio-latch-driver/20220831-135855
base:   https://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux.git gpio/for-next
config: s390-randconfig-r021-20220831 (https://download.01.org/0day-ci/archive/20220901/202209010432.NKyeVosI-lkp@intel.com/config)
compiler: s390-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/8fab8b8c35fd4faebb003751d6d34fc06093c19e
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Sascha-Hauer/gpio-Add-gpio-latch-driver/20220831-135855
        git checkout 8fab8b8c35fd4faebb003751d6d34fc06093c19e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash drivers/gpio/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   drivers/gpio/gpio-latch.c: In function 'gpio_latch_probe':
>> drivers/gpio/gpio-latch.c:163:18: error: 'struct gpio_chip' has no member named 'of_node'; did you mean 'fwnode'?
     163 |         priv->gc.of_node = pdev->dev.of_node;
         |                  ^~~~~~~
         |                  fwnode


vim +163 drivers/gpio/gpio-latch.c

   123	
   124	static int gpio_latch_probe(struct platform_device *pdev)
   125	{
   126		struct gpio_latch_priv *priv;
   127	
   128		priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
   129		if (!priv)
   130			return -ENOMEM;
   131	
   132		priv->clk_gpios = devm_gpiod_get_array(&pdev->dev, "clk", GPIOD_OUT_LOW);
   133		if (IS_ERR(priv->clk_gpios))
   134			return PTR_ERR(priv->clk_gpios);
   135	
   136		priv->data_gpios = devm_gpiod_get_array(&pdev->dev, "data", GPIOD_OUT_LOW);
   137		if (IS_ERR(priv->data_gpios))
   138			return PTR_ERR(priv->data_gpios);
   139	
   140		priv->n_ports = priv->clk_gpios->ndescs;
   141		priv->n_pins = priv->data_gpios->ndescs;
   142	
   143		priv->shadow = devm_kcalloc(&pdev->dev, priv->n_ports, sizeof(*priv->shadow),
   144					    GFP_KERNEL);
   145		if (!priv->shadow)
   146			return -ENOMEM;
   147	
   148		if (gpio_latch_can_sleep(priv)) {
   149			priv->gc.can_sleep = true;
   150			priv->gc.set = gpio_latch_set_can_sleep;
   151			mutex_init(&priv->mutex);
   152		} else {
   153			priv->gc.can_sleep = false;
   154			priv->gc.set = gpio_latch_set;
   155			spin_lock_init(&priv->spinlock);
   156		}
   157	
   158		priv->gc.get_direction = gpio_latch_get_direction;
   159		priv->gc.ngpio = priv->n_ports * priv->n_pins;
   160		priv->gc.owner = THIS_MODULE;
   161		priv->gc.base = -1;
   162		priv->gc.parent = &pdev->dev;
 > 163		priv->gc.of_node = pdev->dev.of_node;
   164	
   165		platform_set_drvdata(pdev, priv);
   166	
   167		return devm_gpiochip_add_data(&pdev->dev, &priv->gc, priv);
   168	}
   169	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Sascha Hauer]

On Wed, Aug 31, 2022 at 11:50:47PM +0300, Andy Shevchenko wrote:
> On Wed, Aug 31, 2022 at 9:02 AM Sascha Hauer <s.hauer@pengutronix.de> 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.
> 
> I'm still unsure it shouldn't be a part of the (not yet in upstream)
> driver that I have mentioned before. But let's leave this apart right
> now.

I don't see how this could be done. The before mentioned driver depends
on a gpio-mux which is a binary decoder. This doesn't have a
correspondence in this driver.

> 
> ...
> 
> > +#include <linux/err.h>
> > +#include <linux/module.h>
> 
> > +#include <linux/of_device.h>
> 
> Why?
> It seems you misplaced it instead of mod_devicetable.h.

Ok.

> 
> > +#include <linux/gpio/driver.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/gpio/consumer.h>
> 
> Keep above sorted?
> 
> ...
> 
> > +       struct mutex mutex;
> > +       spinlock_t spinlock;
> 
> Checkpatch usually complains if locks are not commented. Looking at
> the below code, why it's not an (anonymous) union?

checkpatch only complains here when given a --subjective. Anyway,
commenting it is a good thing, and a union can be used here.

> 
> ...
> 
> > +       if (val)
> > +               priv->shadow[latch] |= BIT(offset % priv->n_pins);
> > +       else
> > +               priv->shadow[latch] &= ~BIT(offset % priv->n_pins);
> 
> I believe shadow should be defined as unsigned long * and hence normal
> bit operations can be applied. For example here is assign_bit().

Good point.

> > +static const struct of_device_id gpio_latch_ids[] = {
> > +       {
> > +               .compatible     = "gpio-latch",
> > +       }, {
> > +               /* sentinel */
> > +       }
> 
> You may compress this to the 2 LoCs.

I usually prefer not doing that as it means that we have to reformat it
once we initialize other fields as well, like here for example .data.

Sascha

-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Andy Shevchenko]

On Wed, Aug 31, 2022 at 9:02 AM Sascha Hauer <s.hauer@pengutronix.de> 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.

So, this is for only one type of latches, now I'm wondering why
gpio-74xx-mmio can't cover this case (with probably small
modifications to the code)?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Sascha Hauer]

On Fri, Sep 02, 2022 at 09:42:21AM +0300, Andy Shevchenko wrote:
> On Wed, Aug 31, 2022 at 9:02 AM Sascha Hauer <s.hauer@pengutronix.de> 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.
> 
> So, this is for only one type of latches, now I'm wondering why
> gpio-74xx-mmio can't cover this case (with probably small
> modifications to the code)?

gpio-74xx-mmio is about latches connected to a parallel bus. You can
access the GPIOs by doing readl/writel operations. The latches are
driven by the bus logic and likely an additional address decoder.

What I have here instead is a latch fully driven by GPIOs.

Yes, with enough force you could implement it in the gpio-74xx-mmio
driver, but that wouldn't be mmio at all and likely completely different
code pathes.

Sascha

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Re: [PATCH v2 1/2] gpio: Add gpio latch driver

[Andy Shevchenko]

On Fri, Sep 2, 2022 at 10:16 AM Sascha Hauer <s.hauer@pengutronix.de> wrote:
> On Fri, Sep 02, 2022 at 09:42:21AM +0300, Andy Shevchenko wrote:
> > On Wed, Aug 31, 2022 at 9:02 AM Sascha Hauer <s.hauer@pengutronix.de> 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.
> >
> > So, this is for only one type of latches, now I'm wondering why
> > gpio-74xx-mmio can't cover this case (with probably small
> > modifications to the code)?
>
> gpio-74xx-mmio is about latches connected to a parallel bus. You can
> access the GPIOs by doing readl/writel operations. The latches are
> driven by the bus logic and likely an additional address decoder.
>
> What I have here instead is a latch fully driven by GPIOs.

But this reminds me of some kind of gpio-aggregator with a specific
layer on top. To me it really feels that we are (semi-)reinventing a
wheel between the lines...

> Yes, with enough force you could implement it in the gpio-74xx-mmio
> driver, but that wouldn't be mmio at all and likely completely different
> code pathes.

Got it, thanks for elaboration.

-- 
With Best Regards,
Andy Shevchenko