[PATCH v3 2/2] leds: spi-byte: add single byte SPI LED driver

[oss@c-mauderer.de]

From: Christian Mauderer <oss@c-mauderer.de>

This driver adds support for simple SPI based LED controller which use
only one byte for setting the brightness.

Signed-off-by: Christian Mauderer <oss@c-mauderer.de>
---

Changes compared to v2:
- use "if (ret)" instead of "if (ret != 0)"
- don't initialize ldev-fields with zero
- use devm_led_classdev_register instead of led_classdev_register
- check for error instead of good case with the last if in spi_byte_probe

Changes compared to v1:
- rename ubnt-spi to leds-spi-byte
- rework probe to get all parameters before allocating anything -> error checks
  all collected together and initializing all fields of the device structure is
  more obvious
- fix some unsteady indentations during variable declaration
- rework comment with protocol explanation
- handle case of off_bright > max_bright
- fix spelling in commit message
- mutex_destroy in remove
- change label to use either use the given one without a prefix or a default one


 drivers/leds/Kconfig         |  12 ++++
 drivers/leds/Makefile        |   1 +
 drivers/leds/leds-spi-byte.c | 134 +++++++++++++++++++++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 drivers/leds/leds-spi-byte.c

diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index a72f97fca57b..0866c55e8004 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -766,6 +766,18 @@ config LEDS_NIC78BX
 	  To compile this driver as a module, choose M here: the module
 	  will be called leds-nic78bx.
 
+config LEDS_SPI_BYTE
+	tristate "LED support for SPI LED controller with a single byte"
+	depends on LEDS_CLASS
+	depends on SPI
+	depends on OF
+	help
+	  This option enables support for LED controller which use a single byte
+	  for controlling the brightness. The minimum and maximum value of the
+	  byte can be configured via a device tree. The driver can be used for
+	  example for the microcontroller based LED controller in the Ubiquiti
+	  airCube ISP devices.
+
 comment "LED Triggers"
 source "drivers/leds/trigger/Kconfig"
 
diff --git a/drivers/leds/Makefile b/drivers/leds/Makefile
index 4c1b0054f379..1786d7e2c236 100644
--- a/drivers/leds/Makefile
+++ b/drivers/leds/Makefile
@@ -75,6 +75,7 @@ obj-$(CONFIG_LEDS_PM8058)		+= leds-pm8058.o
 obj-$(CONFIG_LEDS_MLXCPLD)		+= leds-mlxcpld.o
 obj-$(CONFIG_LEDS_MLXREG)		+= leds-mlxreg.o
 obj-$(CONFIG_LEDS_NIC78BX)		+= leds-nic78bx.o
+obj-$(CONFIG_LEDS_SPI_BYTE)		+= leds-spi-byte.o
 obj-$(CONFIG_LEDS_MT6323)		+= leds-mt6323.o
 obj-$(CONFIG_LEDS_LM3692X)		+= leds-lm3692x.o
 obj-$(CONFIG_LEDS_SC27XX_BLTC)		+= leds-sc27xx-bltc.o
diff --git a/drivers/leds/leds-spi-byte.c b/drivers/leds/leds-spi-byte.c
new file mode 100644
index 000000000000..8170b2da497a
--- /dev/null
+++ b/drivers/leds/leds-spi-byte.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Christian Mauderer <oss@c-mauderer.de>
+
+/*
+ * The driver can be used for controllers with a very simple SPI protocol: Only
+ * one byte between an off and a max value (defined by devicetree) will be sent.
+ */
+
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/spi/spi.h>
+#include <linux/mutex.h>
+#include <uapi/linux/uleds.h>
+
+struct spi_byte_led {
+	struct led_classdev	ldev;
+	struct spi_device	*spi;
+	char			name[LED_MAX_NAME_SIZE];
+	struct mutex		mutex;
+	u8			off_value;
+	u8			max_value;
+};
+
+static int spi_byte_brightness_set_blocking(struct led_classdev *dev,
+					    enum led_brightness brightness)
+{
+	struct spi_byte_led *led = container_of(dev, struct spi_byte_led, ldev);
+	u8 value;
+	int ret;
+
+	value = (u8) brightness + led->off_value;
+
+	mutex_lock(&led->mutex);
+	ret = spi_write(led->spi, &value, sizeof(value));
+	mutex_unlock(&led->mutex);
+
+	return ret;
+}
+
+static int spi_byte_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct device_node *child;
+	struct spi_byte_led *led;
+	int ret;
+	const char *default_name = "leds-spi-byte::";
+	const char *name;
+	u8 off_value;
+	u8 max_value;
+
+	if (!dev->of_node)
+		return -ENODEV;
+
+	if (of_get_child_count(dev->of_node) != 1) {
+		dev_err(dev, "Device must have exactly one LED sub-node.");
+		return -EINVAL;
+	}
+	child = of_get_next_child(dev->of_node, NULL);
+
+	ret = of_property_read_string(child, "label", &name);
+	if (ret)
+		name = default_name;
+
+	ret = of_property_read_u8(child, "leds-spi-byte,off-value", &off_value);
+	if (ret) {
+		dev_err(dev, "LED node needs a leds-spi-byte,off-value.");
+		return -EINVAL;
+	}
+
+	ret = of_property_read_u8(child, "leds-spi-byte,max-value", &max_value);
+	if (ret) {
+		dev_err(dev, "LED node needs a leds-spi-byte,max-value.");
+		return -EINVAL;
+	}
+
+	if (off_value >= max_value) {
+		dev_err(dev, "off-value has to be smaller than max-value.");
+		return -EINVAL;
+	}
+
+	led = devm_kzalloc(dev, sizeof(*led), GFP_KERNEL);
+	if (!led)
+		return -ENOMEM;
+
+	led->spi = spi;
+	strlcpy(led->name, name, sizeof(led->name));
+	mutex_init(&led->mutex);
+	led->off_value = off_value;
+	led->max_value = max_value;
+	led->ldev.name = led->name;
+	led->ldev.max_brightness = led->max_value - led->off_value;
+	led->ldev.brightness_set_blocking = spi_byte_brightness_set_blocking;
+	ret = devm_led_classdev_register(&spi->dev, &led->ldev);
+	if (ret)
+		return ret;
+
+	spi_set_drvdata(spi, led);
+
+	return 0;
+}
+
+static int spi_byte_remove(struct spi_device *spi)
+{
+	struct spi_byte_led	*led = spi_get_drvdata(spi);
+
+	led_classdev_unregister(&led->ldev);
+	mutex_destroy(&led->mutex);
+
+	return 0;
+}
+
+static const struct of_device_id spi_byte_dt_ids[] = {
+	{ .compatible = "leds-spi-byte", },
+	{},
+};
+
+MODULE_DEVICE_TABLE(of, spi_byte_dt_ids);
+
+static struct spi_driver spi_byte_driver = {
+	.probe		= spi_byte_probe,
+	.remove		= spi_byte_remove,
+	.driver = {
+		.name		= KBUILD_MODNAME,
+		.of_match_table	= spi_byte_dt_ids,
+	},
+};
+
+module_spi_driver(spi_byte_driver);
+
+MODULE_AUTHOR("Christian Mauderer <oss@c-mauderer.de>");
+MODULE_DESCRIPTION("single byte SPI LED driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("spi:leds-spi-byte");
-- 
2.21.0