[9fans] Plan9 on Pi 3B+

[Brian L. Stuart]

Has anyone tried Plan 9 on the new Pi 3B+?  I've
run into something that confuses me a bit.  First,
it seems you need the new version of start_cd.elf
to bring up the 3B+.  However, with that, the kernel
throws a lock loop error.  In tracking down the loop,
it happens in startcpus() in archbcm2.c.  The code
here looks like:

    for(i = 0; i < ncpu; i++)
        lock(&startlock[i]);
    cachedwbse(startlock, sizeof startlock);
    for(i = 1; i < ncpu; i++) {
        if(startcpu(i) < 0)
            return i;
        lock(&startlock[i]);
        unlock(&startlock[i]);
    }

So we grab a lock on all the CPUs, then drop into
a second loop where we start CPUs 1 to n.  But
in that loop we grab the lock again and then
immediately unlock it.  This is where the lock
loop happens.  Everything seems to continue
to be happy on both a 2 and a 3B+ if I comment
out the lock in the second loop.  But what is the
rationale for the lock in the second loop?  Was
there a reason for putting it there, or was it an
oversight that wasn't exposed until the new boot
code?

Thanks,
BLS