Re: [PATCH v2] iio: chemical: ccs811: Corrected firmware boot/application mode transition

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 17 Feb 2018 16:28:24 +0000
Richard Lai <richard@richardman.com> 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@richardman.com>
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;