iio: cros_ec: Report hwfifo_watermark_max

Report the maximum amount of sample the EC can hold.
This is not tunable, but can be useful for application to find out the
maximum amount of time it can sleep when hwfifo_timeout is set to a
large number.
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c

@@ -22,6 +22,12 @@
 #include <linux/platform_data/cros_ec_sensorhub.h>
 #include <linux/platform_device.h>
 
+/*
+ * Hard coded to the first device to support sensor fifo.  The EC has a 2048
+ * byte fifo and will trigger an interrupt when fifo is 2/3 full.
+ */
+#define CROS_EC_FIFO_SIZE (2048 * 2 / 3)
+
 static char *cros_ec_loc[] = {
 	[MOTIONSENSE_LOC_BASE] = "base",
 	[MOTIONSENSE_LOC_LID] = "lid",
@@ -55,8 +61,15 @@ static int cros_ec_get_host_cmd_version_mask(struct cros_ec_device *ec_dev,
 
 static void get_default_min_max_freq(enum motionsensor_type type,
 				     u32 *min_freq,
-				     u32 *max_freq)
+				     u32 *max_freq,
+				     u32 *max_fifo_events)
 {
+	/*
+	 * We don't know fifo size, set to size previously used by older
+	 * hardware.
+	 */
+	*max_fifo_events = CROS_EC_FIFO_SIZE;
+
 	switch (type) {
 	case MOTIONSENSE_TYPE_ACCEL:
 	case MOTIONSENSE_TYPE_GYRO:
@@ -149,8 +162,21 @@ static IIO_DEVICE_ATTR(hwfifo_timeout, 0644,
 		       cros_ec_sensor_get_report_latency,
 		       cros_ec_sensor_set_report_latency, 0);
 
+static ssize_t hwfifo_watermark_max_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct cros_ec_sensors_core_state *st = iio_priv(indio_dev);
+
+	return sprintf(buf, "%d\n", st->fifo_max_event_count);
+}
+
+static IIO_DEVICE_ATTR_RO(hwfifo_watermark_max, 0);
+
 const struct attribute *cros_ec_sensor_fifo_attributes[] = {
 	&iio_dev_attr_hwfifo_timeout.dev_attr.attr,
+	&iio_dev_attr_hwfifo_watermark_max.dev_attr.attr,
 	NULL,
 };
 EXPORT_SYMBOL_GPL(cros_ec_sensor_fifo_attributes);
@@ -279,12 +305,15 @@ int cros_ec_sensors_core_init(struct platform_device *pdev,
 		if (state->msg->version < 3) {
 			get_default_min_max_freq(state->resp->info.type,
 						 &state->frequencies[1],
-						 &state->frequencies[2]);
+						 &state->frequencies[2],
+						 &state->fifo_max_event_count);
 		} else {
 			state->frequencies[1] =
 			    state->resp->info_3.min_frequency;
 			state->frequencies[2] =
 			    state->resp->info_3.max_frequency;
+			state->fifo_max_event_count =
+			    state->resp->info_3.fifo_max_event_count;
 		}
 
 		if (cros_ec_check_features(ec, EC_FEATURE_MOTION_SENSE_FIFO)) {

include/linux/iio/common/cros_ec_sensors_core.h

@@ -50,6 +50,7 @@ typedef irqreturn_t (*cros_ec_sensors_capture_t)(int irq, void *p);
  *				the timestamp. The timestamp is always last and
  *				is always 8-byte aligned.
  * @read_ec_sensors_data:	function used for accessing sensors values
+ * @fifo_max_event_count:	Size of the EC sensor FIFO
  */
 struct cros_ec_sensors_core_state {
 	struct cros_ec_device *ec;
@@ -72,6 +73,8 @@ struct cros_ec_sensors_core_state {
 	int (*read_ec_sensors_data)(struct iio_dev *indio_dev,
 				    unsigned long scan_mask, s16 *data);
 
+	u32 fifo_max_event_count;
+
 	/* Table of known available frequencies : 0, Min and Max in mHz */
 	int frequencies[3];
 };