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Comment by philwelch | Hacker News Reader

I'm not a kernel expert but this seems like something that would be ISA-specific. If you're running a Linux kernel on anything other than a 68k processor, this code won't even be there for the most part. And if you are running it on a 68k, odds are you're running it on an old Mac anyway.

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That's more or less correct. The relevant Kconfig is:

  if MACINTOSH_DRIVERS

  config ADB
        bool "Apple Desktop Bus (ADB) support"
        depends on MAC || (PPC_PMAC && PPC32)
        help
          Apple Desktop Bus (ADB) support is for support of devices which
          are connected to an ADB port.  ADB devices tend to have 4 pins.
          If you have an Apple Macintosh prior to the iMac, an iBook or
          PowerBook, or a "Blue and White G3", you probably want to say Y
          here.  Otherwise say N.

In other words, the code is only built into the kernel on architectures where it is useful.

I doubt that it's per-ISA; it's probably by device or maybe bus/transport. That is, with the right adapter you should be able to plug an ADB keyboard into a normal x86 box and have it work, but Linux will only actually load a driver if 1. it's statically compiled in (rare unless you built your own kernel), 2. you explicitly load it (`modprobe foo`), or 3. you plug in a device that uses that driver.

As a reference point, I know NetBSD explicitly decouples these things; if you plug a brand-new PCI device into any system with a PCI slot, NetBSD doesn't care that you're plugging ex. a Sun keyboard into a "PC" USB card in a PowerPC mac - it has a keyboard driver, a USB driver, a PCI driver, and all of them use the same internal interfaces regardless of where they originated. I assume Linux does it the same way, but I don't know explicitly.

The driver code seems to be under “macintosh/via-macii”, for whatever that’s worth.

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