[XenPPC] [PATCH/RFC] Handshake with secondary processors

[Amos Waterland <apw@xxxxxxxxxx>]

This is a rough first cut at handshaking with the secondary processors.
Once we get this right, they will wait on a shared variable, build a
stack, and start running C code proper.  I am posting this now because I
want to make sure we get the register flushes and memory barriers
correct.  Any comments?

The code prints output like this on a JS21:

 spinning up secondary processor #1: ping = 0: pong = 1
 spinning up secondary processor #2: ping = 0: pong = 2
 spinning up secondary processor #3: ping = 0: pong = 3

---

 boot_of.c              |   33 ++++++++++++++++++++++++++++++++-
 powerpc64/exceptions.S |   23 +++++++++++++++++++----
 2 files changed, 51 insertions(+), 5 deletions(-)

diff -r 058f2e27476d xen/arch/powerpc/boot_of.c
--- a/xen/arch/powerpc/boot_of.c        Mon Aug 07 17:49:16 2006 -0500
+++ b/xen/arch/powerpc/boot_of.c        Wed Aug 09 23:08:03 2006 -0400
@@ -42,6 +42,7 @@ static char builtin_cmdline[COMMAND_LINE
     __attribute__((section("__builtin_cmdline"))) = CMDLINE;
 
 extern struct ns16550_defaults ns16550;
+extern unsigned long __spin_ack;
 
 #undef OF_DEBUG
 
@@ -956,7 +957,37 @@ static int __init boot_of_cpus(void)
     /* FIXME: should not depend on the boot CPU bring the first child */
     cpu = of_getpeer(cpu);
     while (cpu > 0) {
-        of_start_cpu(cpu, (ulong)spin_start, 0);
+        unsigned int cpuid;
+        unsigned long ping, pong, now, then, timeout;
+        unsigned long *ack = (unsigned long *)&__spin_ack;
+
+        result = of_getprop(cpu, "reg", &cpuid, sizeof(cpuid));
+        if (result == OF_FAILURE) of_panic("cpuid lookup failed\n");
+
+        of_printf("spinning up secondary processor #%d: ", cpuid);
+
+        *ack = 0x0;
+        ping = *ack;
+        of_printf("ping = %lx: ", ping);
+
+        mb();
+        of_start_cpu(cpu, (ulong)spin_start, cpuid);
+
+        then = mftb();
+        timeout = then + 1024;
+        do {
+            now = mftb();
+            if (now >= timeout) {
+                of_printf("SKIPPING: ");
+                pong = ~0x0;
+                break;
+            }
+
+            mb();
+            pong = *ack;
+        } while (pong == ping);
+        of_printf("pong = %lx\n", pong);
+
         cpu = of_getpeer(cpu);
     }
     return 1;
diff -r 058f2e27476d xen/arch/powerpc/powerpc64/exceptions.S
--- a/xen/arch/powerpc/powerpc64/exceptions.S   Mon Aug 07 17:49:16 2006 -0500
+++ b/xen/arch/powerpc/powerpc64/exceptions.S   Wed Aug 09 21:41:16 2006 -0400
@@ -178,6 +178,25 @@ zero:
     li r0, 0x0 /* exception vector for GDB stub */
     bctr
 
+/* Begin secondary processor spin and ack logic.  */
+    .globl __spin_ack
+__spin_ack:
+    .llong 0x0
+       
+    .globl spin_start
+spin_start:
+    /* Our physical cpu number is passed in r3.  */
+    mr r24, r3
+    lis r25, __spin_ack@highest
+    ori r25, r25, __spin_ack@higher
+    rldicr r25, r25, 32, 31
+    oris r25, r25, __spin_ack@h
+    ori r25, r25, __spin_ack@l
+    stdu r24, 0(r25)
+    sync
+    b .
+
+/* Begin exception handlers.  */       
     . = 0x100 # System Reset
 ex_reset:
     /* XXX thread initialization */
@@ -513,7 +532,3 @@ _GLOBAL(sleep)
     isync
     mtmsrd r3
     blr
-
-    .globl spin_start
-spin_start:
-    b .

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