Add support for /dev/spidev<bus>.<cs> in-kernel SPI CS handling, and convert
existing SPI devices over.
* Add a new member _subdev to the LinuxSPIDeviceDriver class, and initialiser
in LinuxSPIDevice constructor. Use subdev 0 for GPIO-managed CS
* Extend the _cs_pin to signed 16 bits and define SPI_CS_KERNEL (-1) for
kernel-managed CS
* Move to per-device file descriptors (required for in-kernel CS)
* Extend spidev filenames to include bus and subdevice numbers, possibly
longer than 1 digit each
* Allow support for platforms enumerating /dev/spidevNNN from non-zero bases
* Convert existing users over to the new API
Signed-off-by: John Williams <john@whelanwilliams.net>
This adds a check for trying to assert two CS pins on the same bus
at the same time. The change involves moving the _device handles into the
DeviceManager class, and accessing via static methods.
This also moves the semaphore to be per-bus rather than per-device,
which fixes the problem with bad MS5611 transfers.
Pair-Programmed-With: Victor, Sid, Anuj and Philip
John Williams
Staroselskii Georgii
Andrew Tridgell
Mikhail Avkhimenia
Víctor Mayoral Vilches