[RFC PATCH 06/23] ASoC: codecs: wsa884x: register the die temperature as a thermal zone

[Srinivas Kandagatla]

Speaker protection pairs each speaker's calibrated resistance with the
amplifier die temperature (T0) at the time, but an in-kernel user has
no way to read that temperature.

Register a tripless thermal zone over the existing temperature read,
named "wsa-<bus id>-<unique id>" so a user holding the codec's device
can find it with thermal_zone_get_zone_by_name(). Until the codec is
initialised, and while the PA is on with nothing cached yet, return
-EAGAIN to hwmon and no valid temperature to the thermal zone, instead
of a plausible looking zero. -EAGAIN would make the thermal core re-read
the zone every 250 ms and keep the codec awake.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxxxxxxxx>
---
 sound/soc/codecs/wsa884x.c | 70 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/sound/soc/codecs/wsa884x.c b/sound/soc/codecs/wsa884x.c
index fbb9c5773aa5..ecc6983bb54e 100644
--- a/sound/soc/codecs/wsa884x.c
+++ b/sound/soc/codecs/wsa884x.c
@@ -23,6 +23,7 @@
 #include <linux/soundwire/sdw_type.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>
+#include <linux/thermal.h>
 #include <sound/soc-dapm.h>
 #include <sound/soc.h>
 #include <sound/tlv.h>
@@ -1928,8 +1929,10 @@ static int wsa884x_get_temp(struct wsa884x_priv *wsa884x, long *temp)
 	if (wsa884x->pa_on) {
 		/*
 		 * Reading temperature is possible only when Power Amplifier is
-		 * off. Report last cached data.
+		 * off. Report last cached data if we have one, -EAGAIN otherwise.
 		 */
+		if (!wsa884x->temperature)
+			return -EAGAIN;
 		*temp = wsa884x->temperature * 1000;
 		return 0;
 	}
@@ -2051,6 +2054,42 @@ static const struct hwmon_chip_info wsa884x_hwmon_chip_info = {
 	.info	= wsa884x_hwmon_info,
 };
 
+static int wsa884x_tz_get_temp(struct thermal_zone_device *tz, int *temp_mdeg)
+{
+	struct wsa884x_priv *wsa884x = thermal_zone_device_priv(tz);
+	long mdeg;
+	int ret;
+
+	/*
+	 * OTP trims read back as zero until the codec is initialised. Report
+	 * no reading rather than -EAGAIN, which makes the core poll the zone.
+	 */
+	if (!wsa884x->hw_init) {
+		*temp_mdeg = THERMAL_TEMP_INVALID;
+		return 0;
+	}
+
+	ret = wsa884x_get_temp(wsa884x, &mdeg);
+	if (ret == -EAGAIN) {
+		*temp_mdeg = THERMAL_TEMP_INVALID;
+		return 0;
+	}
+	if (ret)
+		return ret;
+
+	*temp_mdeg = (int)mdeg;
+	return 0;
+}
+
+static const struct thermal_zone_device_ops wsa884x_tz_ops = {
+	.get_temp = wsa884x_tz_get_temp,
+};
+
+static void wsa884x_tz_unregister(void *data)
+{
+	thermal_zone_device_unregister(data);
+}
+
 static void wsa884x_reset_powerdown(void *data)
 {
 	struct wsa884x_priv *wsa884x = data;
@@ -2187,6 +2226,35 @@ static int wsa884x_probe(struct sdw_slave *pdev,
 	if (ret)
 		return ret;
 
+	if (IS_REACHABLE(CONFIG_THERMAL)) {
+		char tz_name[THERMAL_NAME_LENGTH];
+		struct thermal_zone_device *tz;
+
+		/*
+		 * Register after runtime PM is enabled, as the zone is read
+		 * right away. dev_name() is too long for a zone name.
+		 */
+		scnprintf(tz_name, sizeof(tz_name), "wsa-%d-%u",
+			  pdev->bus->id, pdev->id.unique_id);
+		tz = thermal_tripless_zone_device_register(tz_name,
+							   wsa884x,
+							   &wsa884x_tz_ops,
+							   NULL);
+		if (IS_ERR(tz)) {
+			dev_warn(dev,
+				 "thermal zone '%s' registration failed (%ld); SP T0 kcontrol will read 0 for this codec\n",
+				 tz_name, PTR_ERR(tz));
+		} else {
+			ret = devm_add_action_or_reset(dev,
+						       wsa884x_tz_unregister,
+						       tz);
+			if (ret)
+				return ret;
+
+			thermal_zone_device_enable(tz);
+		}
+	}
+
 	return devm_snd_soc_register_component(dev,
 					       &wsa884x_component_drv,
 					       wsa884x_dais,
-- 
2.47.3