CCS811 has different I2C register maps in boot and application mode. When CCS811 is in boot mode, register APP_START (0xF4) is used to transit the firmware state from boot to application mode. However, APP_START is not a valid register location when CCS811 is in application mode (refer to "CCS811 Bootloader Register Map" and "CCS811 Application Register Map" in CCS811 datasheet). The driver should not attempt to perform a write to APP_START while CCS811 is in application mode, as this is not a valid or documented register location. When prob function is being called, the driver assumes the CCS811 sensor is in boot mode, and attempts to perform a write to APP_START. Although CCS811 powers-up in boot mode, it may have already been transited to application mode by previous instances, e.g. unload and reload device driver by the system, or explicitly by user. Depending on the system design, CCS811 sensor may be permanently connected to system power source rather than power controlled by GPIO, hence it is possible that the sensor is never power reset, thus the firmware could be in either boot or application mode at any given time when driver prob function is being called. This patch checks the STATUS register before attempting to send a write to APP_START. Only if the firmware is not in application mode and has valid firmware application loaded, then it will continue to start transiting the firmware boot to application mode. Signed-off-by: Richard Lai <richard@xxxxxxxxxxxxxx> --- Changes in v2: - Removed unnecessary macros introduced in previous patch drivers/iio/chemical/ccs811.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/iio/chemical/ccs811.c b/drivers/iio/chemical/ccs811.c index 840a6cb..6ad8a42 100644 --- a/drivers/iio/chemical/ccs811.c +++ b/drivers/iio/chemical/ccs811.c @@ -129,6 +129,9 @@ static int ccs811_start_sensor_application(struct i2c_client *client) if (ret < 0) return ret; + if ((ret & CCS811_STATUS_FW_MODE_APPLICATION)) + return 0; + if ((ret & CCS811_STATUS_APP_VALID_MASK) != CCS811_STATUS_APP_VALID_LOADED) return -EIO; -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
