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commit b91e146c38b003c899710ede6d05fc824675e386 upstream. 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> Cc: <Stable@vger.kernel.org> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.