iio:chemical:bme680: Fix SPI read interface
commit 73f3bc6da506711302bb67572440eb84b1ec4a2c upstream. The SPI interface implementation was completely broken. When using the SPI interface, there are only 7 address bits, the upper bit is controlled by a page select register. The core needs access to both ranges, so implement register read/write for both regions. The regmap paging functionality didn't agree with a register that needs to be read and modified, so I implemented a custom paging algorithm. This fixes that the device wouldn't even probe in SPI mode. The SPI interface then isn't different from I2C, merged them into the core, and the I2C/SPI named registers are no longer needed. Implemented register value caching for the registers to reduce the I2C/SPI data transfers considerably. The calibration set reads as all zeroes until some undefined point in time, and I couldn't determine what makes it valid. The datasheet mentions these registers but does not provide any hints on when they become valid, and they aren't even enumerated in the memory map. So check the calibration and retry reading it from the device after each measurement until it provides something valid. Despite the size this is suitable for a stable backport given that it seems the SPI support never worked. Signed-off-by: NMike Looijmans <mike.looijmans@topic.nl> Fixes: 1b3bd859 ("iio: chemical: Add support for Bosch BME680 sensor"); Cc: <Stable@vger.kernel.org> Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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