On Sat, 17 Feb 2018 16:28:24 +0000 Richard Lai <richard@xxxxxxxxxxxxxx> wrote: > 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> Applied to the fixes-togreg branch of iio.git and marked for stable. Thanks, Jonathan > --- > 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; -- 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
