thermal: int340x: Add keep alive response method

When firmware requests keep alive response, send an event to user space
to confirm by using imok sysfs entry.

Create a new sysf entry called "imok". User space can write an integer,
which results in execution of IMOK ACPI method of INT3400 thermal zone
device. This results in sending response to firmware request for keep
alive.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200915223650.406046-4-srinivas.pandruvada@linux.intel.com

drivers/thermal/intel/int340x_thermal/int3400_thermal.c

@@ -14,6 +14,7 @@
 
 #define INT3400_THERMAL_TABLE_CHANGED 0x83
 #define INT3400_ODVP_CHANGED 0x88
+#define INT3400_KEEP_ALIVE 0xA0
 
 enum int3400_thermal_uuid {
 	INT3400_THERMAL_PASSIVE_1,
@@ -83,8 +84,33 @@ static struct bin_attribute *data_attributes[] = {
 	NULL,
 };
 
+static ssize_t imok_store(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct int3400_thermal_priv *priv = dev_get_drvdata(dev);
+	acpi_status status;
+	int input, ret;
+
+	ret = kstrtouint(buf, 10, &input);
+	if (ret)
+		return ret;
+	status = acpi_execute_simple_method(priv->adev->handle, "IMOK", input);
+	if (ACPI_FAILURE(status))
+		return -EIO;
+
+	return count;
+}
+
+static DEVICE_ATTR_WO(imok);
+
+static struct attribute *imok_attr[] = {
+	&dev_attr_imok.attr,
+	NULL
+};
+
 static const struct attribute_group data_attribute_group = {
 	.bin_attrs = data_attributes,
+	.attrs = imok_attr,
 };
 
 static ssize_t available_uuids_show(struct device *dev,
@@ -358,6 +384,9 @@ static void int3400_notify(acpi_handle handle,
 	case INT3400_THERMAL_TABLE_CHANGED:
 		therm_event = THERMAL_TABLE_CHANGED;
 		break;
+	case INT3400_KEEP_ALIVE:
+		therm_event = THERMAL_EVENT_KEEP_ALIVE;
+		break;
 	case INT3400_ODVP_CHANGED:
 		evaluate_odvp(priv);
 		therm_event = THERMAL_DEVICE_POWER_CAPABILITY_CHANGED;