iio: ad_sigma_delta: Properly handle SPI bus locking vs CS assertion

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For devices from the SigmaDelta family we need to keep CS low when doing a
conversion, since the device will use the MISO line as a interrupt to
indicate that the conversion is complete.

This is why the driver locks the SPI bus and when the SPI bus is locked
keeps as long as a conversion is going on. The current implementation gets
one small detail wrong though. CS is only de-asserted after the SPI bus is
unlocked. This means it is possible for a different SPI device on the same
bus to send a message which would be wrongfully be addressed to the
SigmaDelta device as well. Make sure that the last SPI transfer that is
done while holding the SPI bus lock de-asserts the CS signal.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <Alexandru.Ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

...

This commit is contained in:

Lars-Peter Clausen 2019-03-19 13:37:55 +02:00 • committed by Jonathan Cameron

parent 6ec417d2f1

commit df1d80aee9

2 changed files with 12 additions and 5 deletions

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16

drivers/iio/adc/ad_sigma_delta.c

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1

include/linux/iio/adc/ad_sigma_delta.h

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