platform/chrome: lightbar: Report number of segments

Add attribue `num_segments` to return the number of exposed LED segments
in the lightbar. It can be smaller than the number of physical leds in
the lightbar.

Test: Check the attribute is present and returns a value when read.

Signed-off-by: Gwendal Grignou <gwendal@google.com>
Link: https://lore.kernel.org/r/20260130081351.487517-1-gwendal@google.com
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

Author: gwendalcr

drivers/platform/chrome/cros_ec_lightbar.c

@@ -180,6 +180,47 @@ static ssize_t version_show(struct device *dev,
 	return sysfs_emit(buf, "%d %d\n", version, flags);
 }
 
+static ssize_t num_segments_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct ec_params_lightbar *param;
+	struct ec_response_lightbar *resp;
+	struct cros_ec_command *msg;
+	struct cros_ec_dev *ec = to_cros_ec_dev(dev);
+	uint32_t num = 0;
+	int ret;
+
+	ret = lb_throttle();
+	if (ret)
+		return ret;
+
+	msg = alloc_lightbar_cmd_msg(ec);
+	if (!msg)
+		return -ENOMEM;
+
+	param = (struct ec_params_lightbar *)msg->data;
+	param->cmd = LIGHTBAR_CMD_GET_PARAMS_V3;
+	msg->outsize = sizeof(param->cmd);
+	msg->insize = sizeof(resp->get_params_v3);
+	ret = cros_ec_cmd_xfer_status(ec->ec_dev, msg);
+	if (ret < 0 && ret != -EINVAL)
+		goto exit;
+
+	if (msg->result == EC_RES_SUCCESS) {
+		resp = (struct ec_response_lightbar *)msg->data;
+		num = resp->get_params_v3.reported_led_num;
+	}
+
+	/*
+	 * Anything else (ie, EC_RES_INVALID_COMMAND) - no direct control over
+	 * LEDs, return that no leds are supported.
+	 */
+	ret = sysfs_emit(buf, "%u\n", num);
+exit:
+	kfree(msg);
+	return ret;
+}
+
 static ssize_t brightness_store(struct device *dev,
 				struct device_attribute *attr,
 				const char *buf, size_t count)
@@ -512,6 +553,7 @@ static ssize_t userspace_control_store(struct device *dev,
 /* Module initialization */
 
 static DEVICE_ATTR_RW(interval_msec);
+static DEVICE_ATTR_RO(num_segments);
 static DEVICE_ATTR_RO(version);
 static DEVICE_ATTR_WO(brightness);
 static DEVICE_ATTR_WO(led_rgb);
@@ -521,6 +563,7 @@ static DEVICE_ATTR_RW(userspace_control);
 
 static struct attribute *__lb_cmds_attrs[] = {
 	&dev_attr_interval_msec.attr,
+	&dev_attr_num_segments.attr,
 	&dev_attr_version.attr,
 	&dev_attr_brightness.attr,
 	&dev_attr_led_rgb.attr,

include/linux/platform_data/cros_ec_commands.h

@@ -2005,6 +2005,14 @@ struct lightbar_params_v2_colors {
 	struct rgb_s color[8];			/* 0-3 are Google colors */
 } __ec_todo_packed;
 
+struct lightbar_params_v3 {
+	/*
+	 *  Number of LEDs reported by the EC.
+	 *  May be less than the actual number of LEDs in the lightbar.
+	 */
+	uint8_t reported_led_num;
+} __ec_todo_packed;
+
 /* Lightbar program. */
 #define EC_LB_PROG_LEN 192
 struct lightbar_program {
@@ -2086,6 +2094,8 @@ struct ec_response_lightbar {
 		struct lightbar_params_v2_thresholds get_params_v2_thlds;
 		struct lightbar_params_v2_colors get_params_v2_colors;
 
+		struct lightbar_params_v3 get_params_v3;
+
 		struct __ec_todo_unpacked {
 			uint32_t num;
 			uint32_t flags;
@@ -2143,6 +2153,7 @@ enum lightbar_command {
 	LIGHTBAR_CMD_SET_PARAMS_V2_THRESHOLDS = 31,
 	LIGHTBAR_CMD_GET_PARAMS_V2_COLORS = 32,
 	LIGHTBAR_CMD_SET_PARAMS_V2_COLORS = 33,
+	LIGHTBAR_CMD_GET_PARAMS_V3 = 34,
 	LIGHTBAR_NUM_CMDS
 };