[PATCH] platform: chromeos: sensorhub: retries when a sensor is not ready

[Gwendal Grignou <gwendal@chromium.org>]

When the EC/ISH starts, it can take a while for all the sensors to be up
and running or declared broken.

If the sensor stack return -EBUSY when checking for sensor information,
retry up to 50 times.
It has been observed 100ms wait time is enough to have valid sensors
ready. It can take more time in case a sensor is really broken and is
not coming up.

Signed-off-by: Gwendal Grignou <gwendal@google.com>
---
 drivers/platform/chrome/cros_ec_sensorhub.c | 23 +++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_sensorhub.c b/drivers/platform/chrome/cros_ec_sensorhub.c
index 518152cb4ee10..c246640a9e7e7 100644
--- a/drivers/platform/chrome/cros_ec_sensorhub.c
+++ b/drivers/platform/chrome/cros_ec_sensorhub.c
@@ -8,6 +8,7 @@
 
 #include <linux/init.h>
 #include <linux/device.h>
+#include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/platform_data/cros_ec_commands.h>
 #include <linux/platform_data/cros_ec_proto.h>
@@ -17,6 +18,7 @@
 #include <linux/types.h>
 
 #define DRV_NAME		"cros-ec-sensorhub"
+#define CROS_EC_CMD_INFO_RETRIES 50
 
 static void cros_ec_sensorhub_free_sensor(void *arg)
 {
@@ -52,7 +54,7 @@ static int cros_ec_sensorhub_register(struct device *dev,
 	int sensor_type[MOTIONSENSE_TYPE_MAX] = { 0 };
 	struct cros_ec_command *msg = sensorhub->msg;
 	struct cros_ec_dev *ec = sensorhub->ec;
-	int ret, i;
+	int ret, i, retries;
 	char *name;
 
 
@@ -64,12 +66,25 @@ static int cros_ec_sensorhub_register(struct device *dev,
 		sensorhub->params->cmd = MOTIONSENSE_CMD_INFO;
 		sensorhub->params->info.sensor_num = i;
 
-		ret = cros_ec_cmd_xfer_status(ec->ec_dev, msg);
+		retries = CROS_EC_CMD_INFO_RETRIES;
+		do {
+			ret = cros_ec_cmd_xfer_status(ec->ec_dev, msg);
+			if (ret == -EBUSY) {
+				/* The EC is still busy initializing sensors. */
+				usleep_range(5000, 6000);
+				retries--;
+			}
+		} while (ret == -EBUSY && retries);
+
 		if (ret < 0) {
-			dev_warn(dev, "no info for EC sensor %d : %d/%d\n",
-				 i, ret, msg->result);
+			dev_err(dev, "no info for EC sensor %d : %d/%d\n",
+				i, ret, msg->result);
 			continue;
 		}
+		if (retries < CROS_EC_CMD_INFO_RETRIES) {
+			dev_warn(dev, "%d retries needed to bring up sensor %d\n",
+				 CROS_EC_CMD_INFO_RETRIES - retries, i);
+		}
 
 		switch (sensorhub->resp->info.type) {
 		case MOTIONSENSE_TYPE_ACCEL:
-- 
2.50.0.rc2.761.g2dc52ea45b-goog