platform/chrome: wilco_ec: Add keyboard backlight LED support

The EC is in charge of controlling the keyboard backlight on
the Wilco platform. We expose a standard LED class device
named platform::kbd_backlight.

Since the EC will never change the backlight level of its own accord,
we don't need to implement a brightness_get() method.
Signed-off-by: Nick Crews <ncrews@chromium.org>
Signed-off-by: Daniel Campello <campello@chromium.org>
Reviewed-by: Daniel Campello <campello@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

drivers/platform/chrome/wilco_ec/Kconfig

 # SPDX-License-Identifier: GPL-2.0-only
 config WILCO_EC
 	tristate "ChromeOS Wilco Embedded Controller"
-	depends on ACPI && X86 && CROS_EC_LPC
+	depends on ACPI && X86 && CROS_EC_LPC && LEDS_CLASS
 	help
 	  If you say Y here, you get support for talking to the ChromeOS
 	  Wilco EC over an eSPI bus. This uses a simple byte-level protocol

drivers/platform/chrome/wilco_ec/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-wilco_ec-objs				:= core.o mailbox.o properties.o sysfs.o
+wilco_ec-objs				:= core.o keyboard_leds.o mailbox.o \
+					   properties.o sysfs.o
 obj-$(CONFIG_WILCO_EC)			+= wilco_ec.o
 wilco_ec_debugfs-objs			:= debugfs.o
 obj-$(CONFIG_WILCO_EC_DEBUGFS)		+= wilco_ec_debugfs.o

drivers/platform/chrome/wilco_ec/core.c

@@ -5,10 +5,6 @@
  * Copyright 2018 Google LLC
  *
  * This is the entry point for the drivers that control the Wilco EC.
- * This driver is responsible for several tasks:
- * - Initialize the register interface that is used by wilco_ec_mailbox()
- * - Create a platform device which is picked up by the debugfs driver
- * - Create a platform device which is picked up by the RTC driver
  */
 
 #include <linux/acpi.h>
@@ -87,6 +83,15 @@ static int wilco_ec_probe(struct platform_device *pdev)
 		goto unregister_debugfs;
 	}
 
+	/* Set up the keyboard backlight LEDs. */
+	ret = wilco_keyboard_leds_init(ec);
+	if (ret < 0) {
+		dev_err(dev,
+			"Failed to initialize keyboard LEDs: %d\n",
+			ret);
+		goto unregister_rtc;
+	}
+
 	ret = wilco_ec_add_sysfs(ec);
 	if (ret < 0) {
 		dev_err(dev, "Failed to create sysfs entries: %d", ret);

drivers/platform/chrome/wilco_ec/keyboard_leds.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Keyboard backlight LED driver for the Wilco Embedded Controller
+ *
+ * Copyright 2019 Google LLC
+ *
+ * Since the EC will never change the backlight level of its own accord,
+ * we don't need to implement a brightness_get() method.
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/leds.h>
+#include <linux/platform_data/wilco-ec.h>
+#include <linux/slab.h>
+
+#define WILCO_EC_COMMAND_KBBL		0x75
+#define WILCO_KBBL_MODE_FLAG_PWM	BIT(1)	/* Set brightness by percent. */
+#define WILCO_KBBL_DEFAULT_BRIGHTNESS   0
+
+struct wilco_keyboard_leds {
+	struct wilco_ec_device *ec;
+	struct led_classdev keyboard;
+};
+
+enum wilco_kbbl_subcommand {
+	WILCO_KBBL_SUBCMD_GET_FEATURES = 0x00,
+	WILCO_KBBL_SUBCMD_GET_STATE    = 0x01,
+	WILCO_KBBL_SUBCMD_SET_STATE    = 0x02,
+};
+
+/**
+ * struct wilco_keyboard_leds_msg - Message to/from EC for keyboard LED control.
+ * @command: Always WILCO_EC_COMMAND_KBBL.
+ * @status: Set by EC to 0 on success, 0xFF on failure.
+ * @subcmd: One of enum wilco_kbbl_subcommand.
+ * @reserved3: Should be 0.
+ * @mode: Bit flags for used mode, we want to use WILCO_KBBL_MODE_FLAG_PWM.
+ * @reserved5to8: Should be 0.
+ * @percent: Brightness in 0-100. Only meaningful in PWM mode.
+ * @reserved10to15: Should be 0.
+ */
+struct wilco_keyboard_leds_msg {
+	u8 command;
+	u8 status;
+	u8 subcmd;
+	u8 reserved3;
+	u8 mode;
+	u8 reserved5to8[4];
+	u8 percent;
+	u8 reserved10to15[6];
+} __packed;
+
+/* Send a request, get a response, and check that the response is good. */
+static int send_kbbl_msg(struct wilco_ec_device *ec,
+			 struct wilco_keyboard_leds_msg *request,
+			 struct wilco_keyboard_leds_msg *response)
+{
+	struct wilco_ec_message msg;
+	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = request;
+	msg.request_size = sizeof(*request);
+	msg.response_data = response;
+	msg.response_size = sizeof(*response);
+
+	ret = wilco_ec_mailbox(ec, &msg);
+	if (ret < 0) {
+		dev_err(ec->dev,
+			"Failed sending keyboard LEDs command: %d", ret);
+		return ret;
+	}
+
+	if (response->status) {
+		dev_err(ec->dev,
+			"EC reported failure sending keyboard LEDs command: %d",
+			response->status);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int set_kbbl(struct wilco_ec_device *ec, enum led_brightness brightness)
+{
+	struct wilco_keyboard_leds_msg request;
+	struct wilco_keyboard_leds_msg response;
+
+	memset(&request, 0, sizeof(request));
+	request.command = WILCO_EC_COMMAND_KBBL;
+	request.subcmd  = WILCO_KBBL_SUBCMD_SET_STATE;
+	request.mode    = WILCO_KBBL_MODE_FLAG_PWM;
+	request.percent = brightness;
+
+	return send_kbbl_msg(ec, &request, &response);
+}
+
+static int kbbl_exist(struct wilco_ec_device *ec, bool *exists)
+{
+	struct wilco_keyboard_leds_msg request;
+	struct wilco_keyboard_leds_msg response;
+	int ret;
+
+	memset(&request, 0, sizeof(request));
+	request.command = WILCO_EC_COMMAND_KBBL;
+	request.subcmd  = WILCO_KBBL_SUBCMD_GET_FEATURES;
+
+	ret = send_kbbl_msg(ec, &request, &response);
+	if (ret < 0)
+		return ret;
+
+	*exists = response.status != 0xFF;
+
+	return 0;
+}
+
+/**
+ * kbbl_init() - Initialize the state of the keyboard backlight.
+ * @ec: EC device to talk to.
+ *
+ * Gets the current brightness, ensuring that the BIOS already initialized the
+ * backlight to PWM mode. If not in PWM mode, then the current brightness is
+ * meaningless, so set the brightness to WILCO_KBBL_DEFAULT_BRIGHTNESS.
+ *
+ * Return: Final brightness of the keyboard, or negative error code on failure.
+ */
+static int kbbl_init(struct wilco_ec_device *ec)
+{
+	struct wilco_keyboard_leds_msg request;
+	struct wilco_keyboard_leds_msg response;
+	int ret;
+
+	memset(&request, 0, sizeof(request));
+	request.command = WILCO_EC_COMMAND_KBBL;
+	request.subcmd  = WILCO_KBBL_SUBCMD_GET_STATE;
+
+	ret = send_kbbl_msg(ec, &request, &response);
+	if (ret < 0)
+		return ret;
+
+	if (response.mode & WILCO_KBBL_MODE_FLAG_PWM)
+		return response.percent;
+
+	ret = set_kbbl(ec, WILCO_KBBL_DEFAULT_BRIGHTNESS);
+	if (ret < 0)
+		return ret;
+
+	return WILCO_KBBL_DEFAULT_BRIGHTNESS;
+}
+
+static int wilco_keyboard_leds_set(struct led_classdev *cdev,
+				   enum led_brightness brightness)
+{
+	struct wilco_keyboard_leds *wkl =
+		container_of(cdev, struct wilco_keyboard_leds, keyboard);
+	return set_kbbl(wkl->ec, brightness);
+}
+
+int wilco_keyboard_leds_init(struct wilco_ec_device *ec)
+{
+	struct wilco_keyboard_leds *wkl;
+	bool leds_exist;
+	int ret;
+
+	ret = kbbl_exist(ec, &leds_exist);
+	if (ret < 0) {
+		dev_err(ec->dev,
+			"Failed checking keyboard LEDs support: %d", ret);
+		return ret;
+	}
+	if (!leds_exist)
+		return 0;
+
+	wkl = devm_kzalloc(ec->dev, sizeof(*wkl), GFP_KERNEL);
+	if (!wkl)
+		return -ENOMEM;
+
+	wkl->ec = ec;
+	wkl->keyboard.name = "platform::kbd_backlight";
+	wkl->keyboard.max_brightness = 100;
+	wkl->keyboard.flags = LED_CORE_SUSPENDRESUME;
+	wkl->keyboard.brightness_set_blocking = wilco_keyboard_leds_set;
+	ret = kbbl_init(ec);
+	if (ret < 0)
+		return ret;
+	wkl->keyboard.brightness = ret;
+
+	return devm_led_classdev_register(ec->dev, &wkl->keyboard);
+}

include/linux/platform_data/wilco-ec.h

@@ -122,6 +122,19 @@ struct wilco_ec_message {
  */
 int wilco_ec_mailbox(struct wilco_ec_device *ec, struct wilco_ec_message *msg);
 
+/**
+ * wilco_keyboard_leds_init() - Set up the keyboard backlight LEDs.
+ * @ec: EC device to query.
+ *
+ * After this call, the keyboard backlight will be exposed through a an LED
+ * device at /sys/class/leds.
+ *
+ * This may sleep because it uses wilco_ec_mailbox().
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int wilco_keyboard_leds_init(struct wilco_ec_device *ec);
+
 /*
  * A Property is typically a data item that is stored to NVRAM
  * by the EC. Each of these data items has an index associated