svn commit: r317976 - stable/11/sys/arm/arm

[Oleksandr Tymoshenko]

Author: gonzo
Date: Mon May  8 20:09:23 2017
New Revision: 317976
URL: https://svnweb.freebsd.org/changeset/base/317976

Log:
  MFC r310791:
  
  [qemu] Fix VERSATILEPB kernel boot in QEMU broken by r300968
  
  QEMU does not implement hardware debug registers so when
  dbg_monitor_is_enabled is called kernel receives "invalid instruction"
  exception. QEMU implements only DIDR register and on read returns all
  zeroes to indicate that it doesn't support other registers. Real
  hardware has Version bits set.

Modified:
  stable/11/sys/arm/arm/debug_monitor.c
Directory Properties:
  stable/11/   (props changed)

Modified: stable/11/sys/arm/arm/debug_monitor.c
==============================================================================
--- stable/11/sys/arm/arm/debug_monitor.c	Mon May  8 19:57:43 2017	(r317975)
+++ stable/11/sys/arm/arm/debug_monitor.c	Mon May  8 20:09:23 2017	(r317976)
@@ -792,10 +792,21 @@ dbg_get_ossr(void)
 static __inline boolean_t
 dbg_arch_supported(void)
 {
+	uint32_t dbg_didr;
 
 	switch (dbg_model) {
 	case ID_DFR0_CP_DEBUG_M_V6:
 	case ID_DFR0_CP_DEBUG_M_V6_1:
+		dbg_didr = cp14_dbgdidr_get();
+		/*
+		 * read-all-zeroes is used by QEMU
+		 * to indicate that ARMv6 debug support
+		 * is not implemented. Real hardware has at
+		 * least version bits set
+		 */
+		if (dbg_didr == 0)
+			return (FALSE);
+		return (TRUE);
 	case ID_DFR0_CP_DEBUG_M_V7:
 	case ID_DFR0_CP_DEBUG_M_V7_1:	/* fall through */
 		return (TRUE);