drivers/leds/leds-spi-byte.c

   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/mod_devicetable.h>
  33 #include <linux/module.h>
  34 #include <linux/mutex.h>
  35 #include <linux/property.h>
  36 #include <linux/spi/spi.h>
  37 #include <uapi/linux/uleds.h>
  38
  39 struct spi_byte_chipdef {
  40         /* SPI byte that will be send to switch the LED off */
  41         u8      off_value;
  42         /* SPI byte that will be send to switch the LED to maximum brightness */
  43         u8      max_value;
  44 };
  45
  46 struct spi_byte_led {
  47         struct led_classdev             ldev;
  48         struct spi_device               *spi;
  49         char                            name[LED_MAX_NAME_SIZE];
  50         struct mutex                    mutex;
  51         const struct spi_byte_chipdef   *cdef;
  52 };
  53
  54 static const struct spi_byte_chipdef ubnt_acb_spi_led_cdef = {
  55         .off_value = 0x0,
  56         .max_value = 0x3F,
  57 };
  58
  59 static int spi_byte_brightness_set_blocking(struct led_classdev *dev,
  60                                             enum led_brightness brightness)
  61 {
  62         struct spi_byte_led *led = container_of(dev, struct spi_byte_led, ldev);
  63         u8 value;
  64         int ret;
  65
  66         value = (u8) brightness + led->cdef->off_value;
  67
  68         mutex_lock(&led->mutex);
  69         ret = spi_write(led->spi, &value, sizeof(value));
  70         mutex_unlock(&led->mutex);
  71
  72         return ret;
  73 }
  74
  75 static int spi_byte_probe(struct spi_device *spi)
  76 {
  77         struct fwnode_handle *child __free(fwnode_handle) = NULL;
  78         struct device *dev = &spi->dev;
  79         struct spi_byte_led *led;
  80         struct led_init_data init_data = {};
  81         enum led_default_state state;
  82         int ret;
  83
  84         if (device_get_child_node_count(dev) != 1) {
  85                 dev_err(dev, "Device must have exactly one LED sub-node.");
  86                 return -EINVAL;
  87         }
  88
  89         led = devm_kzalloc(dev, sizeof(*led), GFP_KERNEL);
  90         if (!led)
  91                 return -ENOMEM;
  92
  93         ret = devm_mutex_init(dev, &led->mutex);
  94         if (ret)
  95                 return ret;
  96
  97         led->spi = spi;
  98         led->cdef = device_get_match_data(dev);
  99         led->ldev.brightness = LED_OFF;
 100         led->ldev.max_brightness = led->cdef->max_value - led->cdef->off_value;
 101         led->ldev.brightness_set_blocking = spi_byte_brightness_set_blocking;
 102
 103         child = device_get_next_child_node(dev, NULL);
 104
 105         state = led_init_default_state_get(child);
 106         if (state == LEDS_DEFSTATE_ON)
 107                 led->ldev.brightness = led->ldev.max_brightness;
 108         spi_byte_brightness_set_blocking(&led->ldev,
 109                                          led->ldev.brightness);
 110
 111         init_data.fwnode = child;
 112         init_data.devicename = "leds-spi-byte";
 113         init_data.default_label = ":";
 114
 115         return devm_led_classdev_register_ext(dev, &led->ldev, &init_data);
 116 }
 117
 118 static const struct of_device_id spi_byte_dt_ids[] = {
 119         { .compatible = "ubnt,acb-spi-led", .data = &ubnt_acb_spi_led_cdef },
 120         {}
 121 };
 122 MODULE_DEVICE_TABLE(of, spi_byte_dt_ids);
 123
 124 static struct spi_driver spi_byte_driver = {
 125         .probe          = spi_byte_probe,
 126         .driver = {
 127                 .name           = KBUILD_MODNAME,
 128                 .of_match_table = spi_byte_dt_ids,
 129         },
 130 };
 131 module_spi_driver(spi_byte_driver);
 132
 133 MODULE_AUTHOR("Christian Mauderer <oss@c-mauderer.de>");
 134 MODULE_DESCRIPTION("single byte SPI LED driver");
 135 MODULE_LICENSE("GPL v2");
 136 MODULE_ALIAS("spi:leds-spi-byte");