It may happen that the MPU6050 is the only hardware
trigger available on your system such as this:
> lsiio
Device 003: hscdtd008a
Device 001: mpu6050
Device 002: gp2ap002
Device 000: ab8500-gpadc
Trigger 000: mpu6050-dev1
And when you want to use it to read periodically from
your magnetometer like this:
> iio_generic_buffer -a -c 100 -n hscdtd008a -t mpu6050-dev1
Then the following happens:
[ 209.951334] Internal error: Oops: 5 [#1] SMP ARM
(...)
[ 209.981969] Hardware name: ST-Ericsson Ux5x0 platform (Device Tree Support)
[ 209.988925] PC is at inv_scan_query_mpu6050+0x8/0xb8
[ 209.993914] LR is at inv_mpu6050_set_enable+0x40/0x194
This is because since we are not using any channels from the
same device, the indio_dev->active_scan_mask is NULL.
Just checking for that and bailing out is however not enough:
we have to enable some kind of FIFO for the readout to work.
So enable the temperature as a dummy FIFO and all works
fine.
Not suitable for backporting to stable. It is an odd corner case
and does not represent a regression.
Fixes: 09a642b785 ("Invensense MPU6050 Device Driver.")
Cc: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Link: https://lore.kernel.org/r/20210322132408.1003443-1-linus.walleij@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
454c219f5d