powerpc/booke: Fix xmon single step on PowerPC Book-E

Prior to the arch/ppc -> arch/powerpc transition, xmon had support for single
stepping on 4xx boards.  The functionality was lost when arch/ppc was removed.
This patch restores single step support for 44x boards, and Book-E in general.
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/xmon/xmon.c

@@ -517,6 +517,15 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 	in_xmon = 0;
 #endif
 
+#ifdef CONFIG_BOOKE
+	if (regs->msr & MSR_DE) {
+		bp = at_breakpoint(regs->nip);
+		if (bp != NULL) {
+			regs->nip = (unsigned long) &bp->instr[0];
+			atomic_inc(&bp->ref_count);
+		}
+	}
+#else
 	if ((regs->msr & (MSR_IR|MSR_PR|MSR_SF)) == (MSR_IR|MSR_SF)) {
 		bp = at_breakpoint(regs->nip);
 		if (bp != NULL) {
@@ -530,7 +539,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
 			}
 		}
 	}
-
+#endif
 	insert_cpu_bpts();
 
 	local_irq_restore(flags);
@@ -894,6 +903,14 @@ cmds(struct pt_regs *excp)
 	}
 }
 
+#ifdef CONFIG_BOOKE
+static int do_step(struct pt_regs *regs)
+{
+	regs->msr |= MSR_DE;
+	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
+	return 1;
+}
+#else
 /*
  * Step a single instruction.
  * Some instructions we emulate, others we execute with MSR_SE set.
@@ -924,6 +941,7 @@ static int do_step(struct pt_regs *regs)
 	regs->msr |= MSR_SE;
 	return 1;
 }
+#endif
 
 static void bootcmds(void)
 {