1// SPDX-License-Identifier: GPL-2.0
  2// Copyright (c) 2019 Christian Mauderer <oss@c-mauderer.de>
  3
  4/*
  5 * The driver supports controllers with a very simple SPI protocol:
  6 * - one LED is controlled by a single byte on MOSI
  7 * - the value of the byte gives the brightness between two values (lowest to
  8 *   highest)
  9 * - no return value is necessary (no MISO signal)
 10 *
 11 * The value for minimum and maximum brightness depends on the device
 12 * (compatible string).
 13 *
 14 * Supported devices:
 15 * - "ubnt,acb-spi-led": Microcontroller (SONiX 8F26E611LA) based device used
 16 *   for example in Ubiquiti airCube ISP. Reverse engineered protocol for this
 17 *   controller:
 18 *   * Higher two bits set a mode. Lower six bits are a parameter.
 19 *   * Mode: 00 -> set brightness between 0x00 (min) and 0x3F (max)
 20 *   * Mode: 01 -> pulsing pattern (min -> max -> min) with an interval. From
 21 *     some tests, the period is about (50ms + 102ms * parameter). There is a
 22 *     slightly different pattern starting from 0x10 (longer gap between the
 23 *     pulses) but the time still follows that calculation.
 24 *   * Mode: 10 -> same as 01 but with only a ramp from min to max. Again a
 25 *     slight jump in the pattern at 0x10.
 26 *   * Mode: 11 -> blinking (off -> 25% -> off -> 25% -> ...) with a period of
 27 *     (105ms * parameter)
 28 *   NOTE: This driver currently only supports mode 00.
 29 */
 30
 31#include <linux/leds.h>
 32#include <linux/module.h>
 33#include <linux/of.h>
 34#include <linux/spi/spi.h>
 35#include <linux/mutex.h>
 36#include <uapi/linux/uleds.h>
 37
 38struct spi_byte_chipdef {
 39	/* SPI byte that will be send to switch the LED off */
 40	u8	off_value;
 41	/* SPI byte that will be send to switch the LED to maximum brightness */
 42	u8	max_value;
 43};
 44
 45struct spi_byte_led {
 46	struct led_classdev		ldev;
 47	struct spi_device		*spi;
 48	char				name[LED_MAX_NAME_SIZE];
 49	struct mutex			mutex;
 50	const struct spi_byte_chipdef	*cdef;
 51};
 52
 53static const struct spi_byte_chipdef ubnt_acb_spi_led_cdef = {
 54	.off_value = 0x0,
 55	.max_value = 0x3F,
 56};
 57
 58static const struct of_device_id spi_byte_dt_ids[] = {
 59	{ .compatible = "ubnt,acb-spi-led", .data = &ubnt_acb_spi_led_cdef },
 60	{},
 61};
 62
 63MODULE_DEVICE_TABLE(of, spi_byte_dt_ids);
 64
 65static int spi_byte_brightness_set_blocking(struct led_classdev *dev,
 66					    enum led_brightness brightness)
 67{
 68	struct spi_byte_led *led = container_of(dev, struct spi_byte_led, ldev);
 69	u8 value;
 70	int ret;
 71
 72	value = (u8) brightness + led->cdef->off_value;
 73
 74	mutex_lock(&led->mutex);
 75	ret = spi_write(led->spi, &value, sizeof(value));
 76	mutex_unlock(&led->mutex);
 77
 78	return ret;
 79}
 80
 81static int spi_byte_probe(struct spi_device *spi)
 82{
 83	struct device_node *child;
 84	struct device *dev = &spi->dev;
 85	struct spi_byte_led *led;
 86	const char *name = "leds-spi-byte::";
 87	const char *state;
 88	int ret;
 89
 90	if (of_get_available_child_count(dev_of_node(dev)) != 1) {
 91		dev_err(dev, "Device must have exactly one LED sub-node.");
 92		return -EINVAL;
 93	}
 94	child = of_get_next_available_child(dev_of_node(dev), NULL);
 95
 96	led = devm_kzalloc(dev, sizeof(*led), GFP_KERNEL);
 97	if (!led)
 98		return -ENOMEM;
 99
100	of_property_read_string(child, "label", &name);
101	strscpy(led->name, name, sizeof(led->name));
102	led->spi = spi;
103	mutex_init(&led->mutex);
104	led->cdef = device_get_match_data(dev);
105	led->ldev.name = led->name;
106	led->ldev.brightness = LED_OFF;
107	led->ldev.max_brightness = led->cdef->max_value - led->cdef->off_value;
108	led->ldev.brightness_set_blocking = spi_byte_brightness_set_blocking;
109
110	state = of_get_property(child, "default-state", NULL);
111	if (state) {
112		if (!strcmp(state, "on")) {
113			led->ldev.brightness = led->ldev.max_brightness;
114		} else if (strcmp(state, "off")) {
115			/* all other cases except "off" */
116			dev_err(dev, "default-state can only be 'on' or 'off'");
117			return -EINVAL;
118		}
119	}
120	spi_byte_brightness_set_blocking(&led->ldev,
121					 led->ldev.brightness);
122
123	ret = devm_led_classdev_register(&spi->dev, &led->ldev);
124	if (ret) {
125		mutex_destroy(&led->mutex);
126		return ret;
127	}
128	spi_set_drvdata(spi, led);
129
130	return 0;
131}
132
133static void spi_byte_remove(struct spi_device *spi)
134{
135	struct spi_byte_led	*led = spi_get_drvdata(spi);
136
137	mutex_destroy(&led->mutex);
138}
139
140static struct spi_driver spi_byte_driver = {
141	.probe		= spi_byte_probe,
142	.remove		= spi_byte_remove,
143	.driver = {
144		.name		= KBUILD_MODNAME,
145		.of_match_table	= spi_byte_dt_ids,
146	},
147};
148
149module_spi_driver(spi_byte_driver);
150
151MODULE_AUTHOR("Christian Mauderer <oss@c-mauderer.de>");
152MODULE_DESCRIPTION("single byte SPI LED driver");
153MODULE_LICENSE("GPL v2");
154MODULE_ALIAS("spi:leds-spi-byte");