esp32/machine_hw_spi: Reject invalid number of bits in constructor.

[agatti]

Summary

This commit adds an extra bit of parameters validation to the SPI bus constructor on ESP32. Passing 0 as the number of bits would trigger a division by zero error when performing read/write operations on an SPI bus created in such a fashion.

This fixes #5910.

Testing

This was tested locally on an ESP32-D0WD:

MicroPython v1.24.0-preview.363.g17d823445.dirty on 2024-10-01; Generic ESP32 module with ESP32
Type "help()" for more information.
>>> import machine
>>> machine.SPI(2, 10000000, sck=10, mosi=20, phase=0, bits=0, firstbit=0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Invalid number of bits (0)
>>> machine.SPI(2, 10000000, sck=10, mosi=20, phase=0, bits=-2, firstbit=0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: Invalid number of bits (-2)
>>> machine.SPI(2, 10000000, sck=10, mosi=20, phase=0, bits=-1, firstbit=0)
SPI(id=2, baudrate=10000000, polarity=0, phase=0, bits=8, firstbit=0, sck=10, mosi=20, miso=19)
>>> 

Trade-offs and Alternatives

This PR fixes the issue on ESP32, but maybe this is still a problems on other ports. I do not have many non-ESP32 boards that are currently supported around here so I can only claim this fixes the ESP32 version of the bug. Given that the bus instances are constructed in platform-specific code then I'd have to fix all of them if they have this specific issue. I've got no problem in doing the fix on other platforms but I may not be able to perform code validation.

[dpgeorge]

I think this should be checked in machine_hw_spi_init_internal(), otherwise you can still make it crash via spi.init(bits=0).

[dpgeorge]

I suggest a message like "invalid bits %d", or just "invalid bits". The latter matches adc.c and machine_i2s.c error messages.

[agatti]

This should be sorted now, I also changed the error message to be in line with the other two cases you mentioned, thanks!

[dpgeorge]

Thanks for updating, looks good now.