kernel: add driver package for WS2812B LEDs

Two WS2812B (NeoPixel) clones are used in Xiaomi Redmi AX6000 as
indicator lights. Add a driver for controlling it using SPI MOSI.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

package/kernel/leds-ws2812b/Makefile

@@ -0,0 +1,34 @@
+#
+# Copyright (C) 2008-2010 OpenWrt.org
+#
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=leds-ws2812b
+PKG_RELEASE:=1
+PKG_LICENSE:=GPL-2.0
+
+include $(INCLUDE_DIR)/package.mk
+
+define KernelPackage/leds-ws2812b
+  SUBMENU:=LED modules
+  TITLE:=Worldsemi WS2812B (NeoPixel) LED support
+  FILES:= \
+	$(PKG_BUILD_DIR)/leds-ws2812b.ko
+  AUTOLOAD:=$(call AutoProbe,leds-ws2812b,1)
+  DEPENDS:=@TARGET_mediatek_filogic
+endef
+
+define KernelPackage/leds-ws2812b/description
+  LED support for driving WS2812B (NeoPixel) using SPI MOSI.
+endef
+
+define Build/Compile
+	$(KERNEL_MAKE) M="$(PKG_BUILD_DIR)" modules
+endef
+
+$(eval $(call KernelPackage,leds-ws2812b))

package/kernel/leds-ws2812b/src/Makefile

@@ -0,0 +1 @@
+obj-m := leds-ws2812b.o

package/kernel/leds-ws2812b/src/leds-ws2812b.c

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+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * WorldSemi WS2812B individually-addressable LED driver using SPI
+ *
+ * Copyright 2022 Chuanhong Guo <gch981213@gmail.com>
+ *
+ * This driver simulates WS2812B protocol using SPI MOSI pin. A one pulse
+ * is transferred as 3'b110 and a zero pulse is 3'b100. For this driver to
+ * work properly, the SPI frequency should be 2.105MHz~2.85MHz and it needs
+ * to transfer all the bytes continuously.
+ */
+
+#include <linux/led-class-multicolor.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/property.h>
+#include <linux/spi/spi.h>
+#include <linux/mutex.h>
+
+#define WS2812B_BYTES_PER_COLOR 3
+#define WS2812B_NUM_COLORS 3
+/* A continuous 0 for 50us+ as the 'reset' signal */
+#define WS2812B_RESET_LEN 18
+
+struct ws2812b_led {
+	struct led_classdev_mc mc_cdev;
+	struct mc_subled subled[WS2812B_NUM_COLORS];
+	int cascade;
+};
+
+struct ws2812b_priv {
+	struct led_classdev ldev;
+	struct spi_device *spi;
+	struct mutex mutex;
+	int num_leds;
+	size_t data_len;
+	u8 *data_buf;
+	struct ws2812b_led leds[];
+};
+
+/**
+ * ws2812b_set_byte - convert a byte of data to 3-byte SPI data for pulses
+ * @priv: pointer to the private data structure
+ * @offset: offset of the target byte in the data stream
+ * @val: 1-byte data to be set
+ *
+ * WS2812B receives a stream of bytes from DI, takes the first 3 byte as LED
+ * brightness and pases the rest to the next LED through the DO pin.
+ * This function assembles a single byte of data to the LED:
+ * A bit is represented with a pulse of specific length. A long pulse is a 1
+ * and a short pulse is a 0.
+ * SPI transfers data continuously, MSB first. We can send 3'b100 to create a
+ * 0 pulse and 3'b110 for a 1 pulse. In this way, a byte of data takes up 3
+ * bytes in a SPI transfer:
+ *  1x0 1x0 1x0 1x0 1x0 1x0 1x0 1x0
+ * Let's rearrange it in 8 bits:
+ *  1x01x01x 01x01x01 x01x01x0
+ * The higher 3 bits, middle 2 bits and lower 3 bits are represented with the
+ * 1st, 2nd and 3rd byte in the SPI transfer respectively.
+ * There are only 8 combinations for 3 bits and 4 for 2 bits, so we can create
+ * a lookup table for the 3 bytes.
+ * e.g. For 0x6b -> 2'b01101011:
+ *  Bit 7-5: 3'b011 -> 10011011 -> 0x9b
+ *  Bit 4-3: 2'b01  -> 01001101 -> 0x4d
+ *  Bit 2-0: 3'b011 -> 00110110 -> 0x36
+ */
+static void ws2812b_set_byte(struct ws2812b_priv *priv, size_t offset, u8 val)
+{
+	/* The lookup table for Bit 7-5 4-3 2-0 */
+	const u8 h3b[] = { 0x92, 0x93, 0x9a, 0x9b, 0xd2, 0xd3, 0xda, 0xdb };
+	const u8 m2b[] = { 0x49, 0x4d, 0x69, 0x6d };
+	const u8 l3b[] = { 0x24, 0x26, 0x34, 0x36, 0xa4, 0xa6, 0xb4, 0xb6 };
+	u8 *p = priv->data_buf + WS2812B_RESET_LEN + (offset * WS2812B_BYTES_PER_COLOR);
+
+	p[0] = h3b[val >> 5]; /* Bit 7-5 */
+	p[1] = m2b[(val >> 3) & 0x3]; /* Bit 4-3 */
+	p[2] = l3b[val & 0x7]; /* Bit 2-0 */
+}
+
+static int ws2812b_set(struct led_classdev *cdev,
+		       enum led_brightness brightness)
+{
+	struct led_classdev_mc *mc_cdev = lcdev_to_mccdev(cdev);
+	struct ws2812b_led *led =
+		container_of(mc_cdev, struct ws2812b_led, mc_cdev);
+	struct ws2812b_priv *priv = dev_get_drvdata(cdev->dev->parent);
+	int ret;
+	int i;
+
+	led_mc_calc_color_components(mc_cdev, brightness);
+
+	mutex_lock(&priv->mutex);
+	for (i = 0; i < WS2812B_NUM_COLORS; i++)
+		ws2812b_set_byte(priv, led->cascade * WS2812B_NUM_COLORS + i,
+				 led->subled[i].brightness);
+	ret = spi_write(priv->spi, priv->data_buf, priv->data_len);
+	mutex_unlock(&priv->mutex);
+
+	return ret;
+}
+
+static int ws2812b_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	int cur_led = 0;
+	struct ws2812b_priv *priv;
+	struct fwnode_handle *led_node;
+	int num_leds, i, cnt, ret;
+
+	num_leds = device_get_child_node_count(dev);
+
+	priv = devm_kzalloc(dev, struct_size(priv, leds, num_leds), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	priv->data_len =
+		num_leds * WS2812B_BYTES_PER_COLOR * WS2812B_NUM_COLORS +
+		WS2812B_RESET_LEN;
+	priv->data_buf = kzalloc(priv->data_len, GFP_KERNEL);
+	if (!priv->data_buf)
+		return -ENOMEM;
+
+	for (i = 0; i < num_leds * WS2812B_NUM_COLORS; i++)
+		ws2812b_set_byte(priv, i, 0);
+
+	mutex_init(&priv->mutex);
+	priv->num_leds = num_leds;
+	priv->spi = spi;
+
+	device_for_each_child_node(dev, led_node) {
+		struct led_init_data init_data = {
+			.fwnode = led_node,
+		};
+		/* WS2812B LEDs usually come with GRB color */
+		u32 color_idx[WS2812B_NUM_COLORS] = {
+			LED_COLOR_ID_GREEN,
+			LED_COLOR_ID_RED,
+			LED_COLOR_ID_BLUE,
+		};
+		u32 cascade;
+
+		ret = fwnode_property_read_u32(led_node, "reg", &cascade);
+		if (ret) {
+			dev_err(dev, "failed to obtain numerical LED index for %s",
+				fwnode_get_name(led_node));
+			goto ERR_UNREG_LEDS;
+		}
+		if (cascade >= num_leds) {
+			dev_err(dev, "LED index of %s is larger than the number of LEDs.",
+				fwnode_get_name(led_node));
+			ret = -EINVAL;
+			goto ERR_UNREG_LEDS;
+		}
+
+		cnt = fwnode_property_count_u32(led_node, "color-index");
+		if (cnt > 0 && cnt <= WS2812B_NUM_COLORS)
+			fwnode_property_read_u32_array(led_node, "color-index",
+						       color_idx, (size_t)cnt);
+
+		priv->leds[cur_led].mc_cdev.subled_info =
+			priv->leds[cur_led].subled;
+		priv->leds[cur_led].mc_cdev.num_colors = WS2812B_NUM_COLORS;
+		priv->leds[cur_led].mc_cdev.led_cdev.max_brightness = 255;
+		priv->leds[cur_led].mc_cdev.led_cdev.brightness_set_blocking = ws2812b_set;
+
+		for (i = 0; i < WS2812B_NUM_COLORS; i++) {
+			priv->leds[cur_led].subled[i].color_index = color_idx[i];
+			priv->leds[cur_led].subled[i].intensity = 255;
+		}
+
+		priv->leds[cur_led].cascade = cascade;
+
+		ret = led_classdev_multicolor_register_ext(
+			dev, &priv->leds[cur_led].mc_cdev, &init_data);
+		if (ret) {
+			dev_err(dev, "registration of %s failed.",
+				fwnode_get_name(led_node));
+			goto ERR_UNREG_LEDS;
+		}
+		cur_led++;
+	}
+
+	spi_set_drvdata(spi, priv);
+
+	return 0;
+ERR_UNREG_LEDS:
+	for (; cur_led >= 0; cur_led--)
+		led_classdev_multicolor_unregister(&priv->leds[cur_led].mc_cdev);
+	mutex_destroy(&priv->mutex);
+	kfree(priv->data_buf);
+	return ret;
+}
+
+static int ws2812b_remove(struct spi_device *spi)
+{
+	struct ws2812b_priv *priv = spi_get_drvdata(spi);
+	int cur_led;
+
+	for (cur_led = priv->num_leds - 1; cur_led >= 0; cur_led--)
+		led_classdev_multicolor_unregister(&priv->leds[cur_led].mc_cdev);
+	kfree(priv->data_buf);
+	mutex_destroy(&priv->mutex);
+
+	return 0;
+}
+
+static const struct spi_device_id ws2812b_spi_ids[] = {
+	{ "ws2812b" },
+	{},
+};
+MODULE_DEVICE_TABLE(spi, ws2812b_spi_ids);
+
+static const struct of_device_id ws2812b_dt_ids[] = {
+	{ .compatible = "worldsemi,ws2812b" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, ws2812b_dt_ids);
+
+static struct spi_driver ws2812b_driver = {
+	.probe		= ws2812b_probe,
+	.remove		= ws2812b_remove,
+	.id_table	= ws2812b_spi_ids,
+	.driver = {
+		.name		= KBUILD_MODNAME,
+		.of_match_table	= ws2812b_dt_ids,
+	},
+};
+
+module_spi_driver(ws2812b_driver);
+
+MODULE_AUTHOR("Chuanhong Guo <gch981213@gmail.com>");
+MODULE_DESCRIPTION("WS2812B LED driver using SPI");
+MODULE_LICENSE("GPL");