gpio: Add support for mcp23008/mcp23017/mcp23s08/mcp23s17 IO expanders

[devivanov_proton.me]

Summary

Add support for mcp23xxx IO expanders, SPI and IIC variants. Interrupt support left out for now.

Test Plan

Tested via gpioctl(1)

[vexeduxr]

The new files (excluding the makefiles) are missing licenses.

sys/conf/files

1737–1738

sys/dev/gpio/mcp23017.c

16

This is unused.

42

Wouldn't buf[1] be uninitialized if sc->npin isn't 16?

65–66

117–131

We traditionally put these here.

sys/dev/gpio/mcp23s17.c

37

Not very familiar with the SPI stuff. Is this guaranteed to work? It looks odd to me.

71–72

105–106

sys/dev/gpio/mcp23xxx.c

78

103

152

I'm confused by this. What does pin direction have to do with toggling the pin?

291

I know this is done elsewhere, but style(9) prohibits it.

[devivanov_proton.me]

Update code for style(9)
Add licenses
Fix pin toggle using sc->dir instead of sc->gpio

[devivanov_proton.me]

sys/dev/gpio/mcp23017.c

42

It should be fine since the upper bits aren't used if npin is not 16, but not 100% sure.
Could default initialise the buffer.

sys/dev/gpio/mcp23s17.c

37

It might actually be driver dependent, if it sends the data before receiving. Might require a discard buffer just in case.

[vexeduxr]

The inline comments are in wildly incorrect places now, I'm not sure if I can fix that.

sys/dev/gpio/mcp23017.c

42

It should be fine since the upper bits aren't used if npin is not 16, but not 100% sure.

They are used either way.

(uint16_t)buf[1] << 8

Could default initialise the buffer.

I think it would be better to explicitly initialize it to zero. Default initialization is a C23 extension. :)

[vexeduxr]

sys/dev/gpio/mcp23017.c

42

I think it would be better to explicitly initialize it to zero. Default initialization is a C23 extension. :)

Correction: empty initialization is a C23 thing.

[devivanov_proton.me]

Zero initialise buffer.