platform/chrome: Add Chrome OS keyboard backlight LEDs support

This is a driver for ACPI-based keyboard backlight LEDs found on
Chromebooks. The driver locates \\_SB.KBLT ACPI device and exports
backlight as "chromeos::kbd_backlight" LED class device in sysfs.

Signed-off-by: Simon Que <[e-mail]>
Signed-off-by: Duncan Laurie <[e-mail]>
Tested-by: Evan McClain <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>
Signed-off-by: Olof Johansson <[e-mail]>

drivers/platform/chrome/Kconfig

···
         help
           ChromeOS EC communication protocol helpers.
 
+config CROS_KBD_LED_BACKLIGHT
+	tristate "Backlight LED support for Chrome OS keyboards"
+	depends on LEDS_CLASS && ACPI
+	help
+	  This option enables support for the keyboard backlight LEDs on
+	  select Chrome OS systems.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called cros_kbd_led_backlight.
+
 endif # CHROMEOS_PLATFORMS

drivers/platform/chrome/Makefile

···
 
-obj-$(CONFIG_CHROMEOS_LAPTOP)	+= chromeos_laptop.o
-obj-$(CONFIG_CHROMEOS_PSTORE)	+= chromeos_pstore.o
-cros_ec_devs-objs		:= cros_ec_dev.o cros_ec_sysfs.o \
-				   cros_ec_lightbar.o cros_ec_vbc.o
-obj-$(CONFIG_CROS_EC_CHARDEV)   += cros_ec_devs.o
-obj-$(CONFIG_CROS_EC_LPC)       += cros_ec_lpc.o
-obj-$(CONFIG_CROS_EC_PROTO)	+= cros_ec_proto.o
+obj-$(CONFIG_CHROMEOS_LAPTOP)		+= chromeos_laptop.o
+obj-$(CONFIG_CHROMEOS_PSTORE)		+= chromeos_pstore.o
+cros_ec_devs-objs			:= cros_ec_dev.o cros_ec_sysfs.o \
+					   cros_ec_lightbar.o cros_ec_vbc.o
+obj-$(CONFIG_CROS_EC_CHARDEV)		+= cros_ec_devs.o
+obj-$(CONFIG_CROS_EC_LPC)		+= cros_ec_lpc.o
+obj-$(CONFIG_CROS_EC_PROTO)		+= cros_ec_proto.o
+obj-$(CONFIG_CROS_KBD_LED_BACKLIGHT)	+= cros_kbd_led_backlight.o

drivers/platform/chrome/cros_kbd_led_backlight.c

···
+/*
+ *  Keyboard backlight LED driver for Chrome OS.
+ *
+ *  Copyright (C) 2012 Google, Inc.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ */
+
+#include <linux/acpi.h>
+#include <linux/leds.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+/* Keyboard LED ACPI Device must be defined in firmware */
+#define ACPI_KEYBOARD_BACKLIGHT_DEVICE	"\\_SB.KBLT"
+#define ACPI_KEYBOARD_BACKLIGHT_READ	ACPI_KEYBOARD_BACKLIGHT_DEVICE ".KBQC"
+#define ACPI_KEYBOARD_BACKLIGHT_WRITE	ACPI_KEYBOARD_BACKLIGHT_DEVICE ".KBCM"
+
+#define ACPI_KEYBOARD_BACKLIGHT_MAX		100
+
+static void keyboard_led_set_brightness(struct led_classdev *cdev,
+					enum led_brightness brightness)
+{
+	union acpi_object param;
+	struct acpi_object_list input;
+	acpi_status status;
+
+	param.type = ACPI_TYPE_INTEGER;
+	param.integer.value = brightness;
+	input.count = 1;
+	input.pointer = &param;
+
+	status = acpi_evaluate_object(NULL, ACPI_KEYBOARD_BACKLIGHT_WRITE,
+				      &input, NULL);
+	if (ACPI_FAILURE(status))
+		dev_err(cdev->dev, "Error setting keyboard LED value: %d\n",
+			status);
+}
+
+static enum led_brightness
+keyboard_led_get_brightness(struct led_classdev *cdev)
+{
+	unsigned long long brightness;
+	acpi_status status;
+
+	status = acpi_evaluate_integer(NULL, ACPI_KEYBOARD_BACKLIGHT_READ,
+				       NULL, &brightness);
+	if (ACPI_FAILURE(status)) {
+		dev_err(cdev->dev, "Error getting keyboard LED value: %d\n",
+			status);
+		return -EIO;
+	}
+
+	return brightness;
+}
+
+static int keyboard_led_probe(struct platform_device *pdev)
+{
+	struct led_classdev *cdev;
+	acpi_handle handle;
+	acpi_status status;
+	int error;
+
+	/* Look for the keyboard LED ACPI Device */
+	status = acpi_get_handle(ACPI_ROOT_OBJECT,
+				 ACPI_KEYBOARD_BACKLIGHT_DEVICE,
+				 &handle);
+	if (ACPI_FAILURE(status)) {
+		dev_err(&pdev->dev, "Unable to find ACPI device %s: %d\n",
+			ACPI_KEYBOARD_BACKLIGHT_DEVICE, status);
+		return -ENXIO;
+	}
+
+	cdev = devm_kzalloc(&pdev->dev, sizeof(*cdev), GFP_KERNEL);
+	if (!cdev)
+		return -ENOMEM;
+
+	cdev->name = "chromeos::kbd_backlight";
+	cdev->max_brightness = ACPI_KEYBOARD_BACKLIGHT_MAX;
+	cdev->flags |= LED_CORE_SUSPENDRESUME;
+	cdev->brightness_set = keyboard_led_set_brightness;
+	cdev->brightness_get = keyboard_led_get_brightness;
+
+	error = devm_led_classdev_register(&pdev->dev, cdev);
+	if (error)
+		return error;
+
+	return 0;
+}
+
+static const struct acpi_device_id keyboard_led_id[] = {
+	{ "GOOG0002", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, keyboard_led_id);
+
+static struct platform_driver keyboard_led_driver = {
+	.driver		= {
+		.name	= "chromeos-keyboard-leds",
+		.acpi_match_table = ACPI_PTR(keyboard_led_id),
+	},
+	.probe		= keyboard_led_probe,
+};
+module_platform_driver(keyboard_led_driver);
+
+MODULE_AUTHOR("Simon Que <[e-mail]>");
+MODULE_DESCRIPTION("ChromeOS Keyboard backlight LED Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:chromeos-keyboard-leds");