inconsistent spidev index on BeagleBone/PocketBeagle

This issue effects boards with the AM3358 chip such as BeagleBone and PocketBeagle. It was discovered while testing #100.

The index in the spidev path can be inconsistent between kernel builds. This means that sometimes SPI0 is /dev/spidev0.x and sometimes SPI0 is /dev/spidev1.x

For example, SPI0 is /dev/spidev1.0 when using the 4.14.108-ti-r103 kernel:

debian@beaglebone:~$ ls -ltar /dev/spidev*
crw-rw---- 1 root spi 153, 0 Apr 12 17:42 /dev/spidev1.0
crw-rw---- 1 root spi 153, 1 Apr 12 17:42 /dev/spidev2.0
crw-rw---- 1 root spi 153, 2 Apr 12 17:42 /dev/spidev2.1

However, SPI0 is /dev/spidev0.0 when using the 4.14.106-bone20 kernel:

debian@beaglebone:~$ ls -la /dev/spidev*
crw-rw---- 1 root spi 153, 0 Apr 13 13:35 /dev/spidev0.0
crw-rw---- 1 root spi 153, 1 Apr 13 13:35 /dev/spidev1.0
crw-rw---- 1 root spi 153, 2 Apr 13 13:35 /dev/spidev1.1

[ladyada]

nice - yes id rather mess with the pins/spi index definition than the core blinka SPI code. lets keep that neat and organized 😃

[pdp7]

@RobertCNelson thanks for the explanation.

@ladyada thanks, your comment made me realize that I can adjust the indexes in spiPorts inside microcontroller/am335x/pin.py

SPI0 is /dev/spidev1.x and SPI1 is /dev/spidev2.x on both:

• the current recommended BeagleBoard.org Debian image: Debian 9.5 (Stretch) from 2018-10-07
• the newest Debian 9.8 (Strecth) snapshot from 2019-04-07

I think spiPorts should changed from:

# ordered as spiId, sckId, mosiId, misoId
spiPorts = (
    (0, SPI0_SCLK, SPI0_D1, SPI0_D0),
    (1, SPI1_SCLK, SPI1_D1, SPI1_D0),
)

to:

# ordered as spiId, sckId, mosiId, misoId
spiPorts = (
    (1, SPI0_SCLK, SPI0_D1, SPI0_D0),
    (2, SPI1_SCLK, SPI1_D1, SPI1_D0),
)

By the way, the new BeagleBone AI should hopefully launch this Summer. It uses a much more powerful TI Sitara AM5729 SoC but keeps the traditional P8/P9 BeagleBone headers. @jadonk has been working on BeagleBone cape interface spec so that we can have consistency between the new and old BeagleBones.