mp.c

// Multiprocessor support
// Search memory for MP description structures.
// http://developer.intel.com/design/pentium/datashts/24201606.pdf

#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mp.h"
#include "x86.h"
#include "mmu.h"
#include "proc.h"

struct cpu cpus[NCPU];
int ncpu;
uchar ioapicid;

static uchar sum(uchar *addr, int len) {
  int i, sum;

  sum = 0;
  for (i = 0; i < len; i++)
    sum += addr[i];
  return sum;
}

// Look for an MP structure in the len bytes at addr.
static struct mp *mpsearch1(uint a, int len) {
  uchar *e, *p, *addr;

  addr = P2V(a);
  e = addr + len;
  for (p = addr; p < e; p += sizeof(struct mp))
    if (memcmp(p, "_MP_", 4) == 0 && sum(p, sizeof(struct mp)) == 0)
      return (struct mp *)p;
  return 0;
}

// Search for the MP Floating Pointer Structure, which according to the
// spec is in one of the following three locations:
// 1) in the first KB of the EBDA;
// 2) in the last KB of system base memory;
// 3) in the BIOS ROM between 0xE0000 and 0xFFFFF.
static struct mp *mpsearch(void) {
  uchar *bda;
  uint p;
  struct mp *mp;

  bda = (uchar *)P2V(0x400);
  if ((p = ((bda[0x0F] << 8) | bda[0x0E]) << 4)) {
    if ((mp = mpsearch1(p, 1024)))
      return mp;
  } else {
    p = ((bda[0x14] << 8) | bda[0x13]) * 1024;
    if ((mp = mpsearch1(p - 1024, 1024)))
      return mp;
  }
  return mpsearch1(0xF0000, 0x10000);
}

// Search for an MP configuration table.  For now,
// don't accept the default configurations (physaddr == 0).
// Check for correct signature, calculate the checksum and,
// if correct, check the version.
// To do: check extended table checksum.
static struct mpconf *mpconfig(struct mp **pmp) {
  struct mpconf *conf;
  struct mp *mp;

  if ((mp = mpsearch()) == 0 || mp->physaddr == 0)
    return 0;
  conf = (struct mpconf *)P2V((uint)mp->physaddr);
  if (memcmp(conf, "PCMP", 4) != 0)
    return 0;
  if (conf->version != 1 && conf->version != 4)
    return 0;
  if (sum((uchar *)conf, conf->length) != 0)
    return 0;
  *pmp = mp;
  return conf;
}

void mpinit(void) {
  uchar *p, *e;
  int ismp;
  struct mp *mp;
  struct mpconf *conf;
  struct mpproc *proc;
  struct mpioapic *ioapic;

  if ((conf = mpconfig(&mp)) == 0)
    panic("Expect to run on an SMP");
  ismp = 1;
  lapic = (uint *)conf->lapicaddr;
  for (p = (uchar *)(conf + 1), e = (uchar *)conf + conf->length; p < e;) {
    switch (*p) {
    case MPPROC:
      proc = (struct mpproc *)p;
      if (ncpu < NCPU) {
        cpus[ncpu].apicid = proc->apicid; // apicid may differ from ncpu
        ncpu++;
      }
      p += sizeof(struct mpproc);
      continue;
    case MPIOAPIC:
      ioapic = (struct mpioapic *)p;
      ioapicid = ioapic->apicno;
      p += sizeof(struct mpioapic);
      continue;
    case MPBUS:
    case MPIOINTR:
    case MPLINTR:
      p += 8;
      continue;
    default:
      ismp = 0;
      break;
    }
  }
  if (!ismp)
    panic("Didn't find a suitable machine");

  if (mp->imcrp) {
    // Bochs doesn't support IMCR, so this doesn't run on Bochs.
    // But it would on real hardware.
    outb(0x22, 0x70);          // Select IMCR
    outb(0x23, inb(0x23) | 1); // Mask external interrupts.
  }
}