powerpc/xmon: Enable HW instruction breakpoint on POWER8

This patch enables support for hardware instruction breakpoint in xmon
on POWER8 platform with the help of a new register called the CIABR
(Completed Instruction Address Breakpoint Register). With this patch, a
single hardware instruction breakpoint can be added and cleared during
any active xmon debug session. The hardware based instruction breakpoint
mechanism works correctly with the existing TRAP based instruction
breakpoint available on xmon.

There are no powerpc CPU with CPU_FTR_IABR feature any more. This patch
has re-purposed all the existing IABR related code to work with CIABR
register based HW instruction breakpoint.

This has one odd feature, which is that when we hit a breakpoint xmon
doesn't tell us we have hit the breakpoint. This is because xmon is
expecting bp->address == regs->nip. Because CIABR fires on completition
regs->nip points to the instruction after the breakpoint. We could fix
that, but it would then confuse other parts of the xmon code which think
we need to emulate the instruction. [mpe]

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>

1 files changed, 51 insertions, 7 deletions

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index ef18021d52e1..820dc135f040 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -51,6 +51,12 @@
 #include <asm/paca.h>
 #endif
 
+#if defined(CONFIG_PPC_SPLPAR)
+#include <asm/plpar_wrappers.h>
+#else
+static inline long plapr_set_ciabr(unsigned long ciabr) {return 0; };
+#endif
+
 #include "nonstdio.h"
 #include "dis-asm.h"
 
@@ -270,6 +276,45 @@ static inline void cinval(void *p)
 	asm volatile ("dcbi 0,%0; icbi 0,%0" : : "r" (p));
 }
 
+/**
+ * write_ciabr() - write the CIABR SPR
+ * @ciabr:	The value to write.
+ *
+ * This function writes a value to the CIARB register either directly
+ * through mtspr instruction if the kernel is in HV privilege mode or
+ * call a hypervisor function to achieve the same in case the kernel
+ * is in supervisor privilege mode.
+ */
+static void write_ciabr(unsigned long ciabr)
+{
+	if (!cpu_has_feature(CPU_FTR_ARCH_207S))
+		return;
+
+	if (cpu_has_feature(CPU_FTR_HVMODE)) {
+		mtspr(SPRN_CIABR, ciabr);
+		return;
+	}
+	plapr_set_ciabr(ciabr);
+}
+
+/**
+ * set_ciabr() - set the CIABR
+ * @addr:	The value to set.
+ *
+ * This function sets the correct privilege value into the the HW
+ * breakpoint address before writing it up in the CIABR register.
+ */
+static void set_ciabr(unsigned long addr)
+{
+	addr &= ~CIABR_PRIV;
+
+	if (cpu_has_feature(CPU_FTR_HVMODE))
+		addr |= CIABR_PRIV_HYPER;
+	else
+		addr |= CIABR_PRIV_SUPER;
+	write_ciabr(addr);
+}
+
 /*
  * Disable surveillance (the service processor watchdog function)
  * while we are in xmon.
@@ -764,9 +809,9 @@ static void insert_cpu_bpts(void)
 		brk.len = 8;
 		__set_breakpoint(&brk);
 	}
-	if (iabr && cpu_has_feature(CPU_FTR_IABR))
-		mtspr(SPRN_IABR, iabr->address
-			 | (iabr->enabled & (BP_IABR|BP_IABR_TE)));
+
+	if (iabr)
+		set_ciabr(iabr->address);
 }
 
 static void remove_bpts(void)
@@ -792,8 +837,7 @@ static void remove_bpts(void)
 static void remove_cpu_bpts(void)
 {
 	hw_breakpoint_disable();
-	if (cpu_has_feature(CPU_FTR_IABR))
-		mtspr(SPRN_IABR, 0);
+	write_ciabr(0);
 }
 
 /* Command interpreting routine */
@@ -1128,7 +1172,7 @@ static char *breakpoint_help_string =
     "b <addr> [cnt]   set breakpoint at given instr addr\n"
     "bc               clear all breakpoints\n"
     "bc <n/addr>      clear breakpoint number n or at addr\n"
-    "bi <addr> [cnt]  set hardware instr breakpoint (POWER3/RS64 only)\n"
+    "bi <addr> [cnt]  set hardware instr breakpoint (POWER8 only)\n"
     "bd <addr> [cnt]  set hardware data breakpoint\n"
     "";
 
@@ -1167,7 +1211,7 @@ bpt_cmds(void)
 		break;
 
 	case 'i':	/* bi - hardware instr breakpoint */
-		if (!cpu_has_feature(CPU_FTR_IABR)) {
+		if (!cpu_has_feature(CPU_FTR_ARCH_207S)) {
 			printf("Hardware instruction breakpoint "
 			       "not supported on this cpu\n");
 			break;