arm: add generic syscon driver

[kevans]

Summary

Upstream dts for allwinner will require a syscon driver, since the emac node coming in 4.15 will be using xref to /soc/syscon for configuring the emac clock. Add a generic syscon driver to attach to /soc/syscon for use by if_awg.

This syscon driver was written by mmel@; I only applied minor style/comment changes and made probe return BUS_PROBE_GENERIC.

Tested on: BananaPi-M3 (a83t)

[bcr]

Typo

sys/arm/arm/syscon_if.m

35 ↗

(On Diff #35965)

s/Accesor/Accessor/

[manu]

This will be used in arm64 and maybe mips ?
Should we put it in sys/dev/ directly instead ?

[andrew]

sys/arm/allwinner/files.allwinner

3–4 ↗

(On Diff #35965)

This should be in sys/conf/files.arm and be optional syscon

[kevans]

In D13295#277602, @manu wrote:

This will be used in arm64 and maybe mips ?
Should we put it in sys/dev/ directly instead ?

That sounds reasonable, but the naming is kind of unfortunate since we have the completely unrelated dev/syscons that's a single character away.

@andrew Do we have documentation on the syntax for files files so that I can make sure I'm doing what I intend to be doing- both here and in dependencies of this thing?

[kevans]

Something like this, perhaps? I'll also need to update D13296 to note dependency on 'syscon' for if_awg.c and add syscon to arm/GENERIC.

sys/arm/arm/syscon_if.m

35 ↗

(On Diff #35965)

Whoops, thanks!

[kevans]

Saw the other half of @andrew's comment; moved files bits to sys/conf/files.arm

[manu]

sys/conf/files.arm

141

Since we're gonna use it on armv7 and arm64 this should be in sys/conf/files with 'optional fdt syscon

[kevans]

Bounce inclusion over to sys/conf/files