[PATCH 2/3] hwmon: surface_temp: Add support for sensor names

[Maximilian Luz <luzmaximilian@gmail.com>]

From: Ivor Wanders <ivor@iwanders.net>

The thermal subsystem of the Surface Aggregator Module allows us to
query the names of the respective thermal sensors. Forward those to
userspace.

Signed-off-by: Ivor Wanders <ivor@iwanders.net>
Co-developed-by: Maximilian Luz <luzmaximilian@gmail.com>
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
---
 drivers/hwmon/surface_temp.c | 112 +++++++++++++++++++++++++++++------
 1 file changed, 95 insertions(+), 17 deletions(-)

diff --git a/drivers/hwmon/surface_temp.c b/drivers/hwmon/surface_temp.c
index 48c3e826713f6..7a2e1f638336c 100644
--- a/drivers/hwmon/surface_temp.c
+++ b/drivers/hwmon/surface_temp.c
@@ -17,6 +17,27 @@
 
 /* -- SAM interface. -------------------------------------------------------- */
 
+/*
+ * Available sensors are indicated by a 16-bit bitfield, where a 1 marks the
+ * presence of a sensor. So we have at most 16 possible sensors/channels.
+ */
+#define SSAM_TMP_SENSOR_MAX_COUNT 16
+
+/*
+ * All names observed so far are 6 characters long, but there's only
+ * zeros after the name, so perhaps they can be longer. This number reflects
+ * the maximum zero-padded space observed in the returned buffer.
+ */
+#define SSAM_TMP_SENSOR_NAME_LENGTH 18
+
+struct ssam_tmp_get_name_rsp {
+	__le16 unknown1;
+	char unknown2;
+	char name[SSAM_TMP_SENSOR_NAME_LENGTH];
+} __packed;
+
+static_assert(sizeof(struct ssam_tmp_get_name_rsp) == 21);
+
 SSAM_DEFINE_SYNC_REQUEST_CL_R(__ssam_tmp_get_available_sensors, __le16, {
 	.target_category = SSAM_SSH_TC_TMP,
 	.command_id      = 0x04,
@@ -27,6 +48,11 @@ SSAM_DEFINE_SYNC_REQUEST_MD_R(__ssam_tmp_get_temperature, __le16, {
 	.command_id      = 0x01,
 });
 
+SSAM_DEFINE_SYNC_REQUEST_MD_R(__ssam_tmp_get_name, struct ssam_tmp_get_name_rsp, {
+	.target_category = SSAM_SSH_TC_TMP,
+	.command_id      = 0x0e,
+});
+
 static int ssam_tmp_get_available_sensors(struct ssam_device *sdev, s16 *sensors)
 {
 	__le16 sensors_le;
@@ -54,12 +80,37 @@ static int ssam_tmp_get_temperature(struct ssam_device *sdev, u8 iid, long *temp
 	return 0;
 }
 
+static int ssam_tmp_get_name(struct ssam_device *sdev, u8 iid, char *buf, size_t buf_len)
+{
+	struct ssam_tmp_get_name_rsp name_rsp;
+	int status;
+
+	status =  __ssam_tmp_get_name(sdev->ctrl, sdev->uid.target, iid, &name_rsp);
+	if (status)
+		return status;
+
+	/*
+	 * This should not fail unless the name in the returned struct is not
+	 * null-terminated or someone changed something in the struct
+	 * definitions above, since our buffer and struct have the same
+	 * capacity by design. So if this fails blow this up with a warning.
+	 * Since the more likely cause is that the returned string isn't
+	 * null-terminated, we might have received garbage (as opposed to just
+	 * an incomplete string), so also fail the function.
+	 */
+	status = strscpy(buf, name_rsp.name, buf_len);
+	WARN_ON(status < 0);
+
+	return status < 0 ? status : 0;
+}
+
 
 /* -- Driver.---------------------------------------------------------------- */
 
 struct ssam_temp {
 	struct ssam_device *sdev;
 	s16 sensors;
+	char names[SSAM_TMP_SENSOR_MAX_COUNT][SSAM_TMP_SENSOR_NAME_LENGTH];
 };
 
 static umode_t ssam_temp_hwmon_is_visible(const void *data,
@@ -83,33 +134,47 @@ static int ssam_temp_hwmon_read(struct device *dev,
 	return ssam_tmp_get_temperature(ssam_temp->sdev, channel + 1, value);
 }
 
+static int ssam_temp_hwmon_read_string(struct device *dev,
+				       enum hwmon_sensor_types type,
+				       u32 attr, int channel, const char **str)
+{
+	const struct ssam_temp *ssam_temp = dev_get_drvdata(dev);
+
+	*str = ssam_temp->names[channel];
+	return 0;
+}
+
 static const struct hwmon_channel_info * const ssam_temp_hwmon_info[] = {
 	HWMON_CHANNEL_INFO(chip,
 			   HWMON_C_REGISTER_TZ),
-	/* We have at most 16 thermal sensor channels. */
+	/*
+	 * We have at most SSAM_TMP_SENSOR_MAX_COUNT = 16 thermal sensor
+	 * channels.
+	 */
 	HWMON_CHANNEL_INFO(temp,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT,
-			   HWMON_T_INPUT),
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL,
+			   HWMON_T_INPUT | HWMON_T_LABEL),
 	NULL
 };
 
 static const struct hwmon_ops ssam_temp_hwmon_ops = {
 	.is_visible = ssam_temp_hwmon_is_visible,
 	.read = ssam_temp_hwmon_read,
+	.read_string = ssam_temp_hwmon_read_string,
 };
 
 static const struct hwmon_chip_info ssam_temp_hwmon_chip_info = {
@@ -122,6 +187,7 @@ static int ssam_temp_probe(struct ssam_device *sdev)
 	struct ssam_temp *ssam_temp;
 	struct device *hwmon_dev;
 	s16 sensors;
+	int channel;
 	int status;
 
 	status = ssam_tmp_get_available_sensors(sdev, &sensors);
@@ -135,6 +201,18 @@ static int ssam_temp_probe(struct ssam_device *sdev)
 	ssam_temp->sdev = sdev;
 	ssam_temp->sensors = sensors;
 
+	/* Retrieve the name for each available sensor. */
+	for (channel = 0; channel < SSAM_TMP_SENSOR_MAX_COUNT; channel++) {
+		if (!(sensors & BIT(channel)))
+			continue;
+
+		status = ssam_tmp_get_name(sdev, channel + 1,
+					   ssam_temp->names[channel],
+					   SSAM_TMP_SENSOR_NAME_LENGTH);
+		if (status)
+			return status;
+	}
+
 	hwmon_dev = devm_hwmon_device_register_with_info(&sdev->dev,
 			"surface_thermal", ssam_temp, &ssam_temp_hwmon_chip_info,
 			NULL);
-- 
2.44.0