tilegx: support KGDB

Enter kernel debugger at boot with:
  --hvd UART_1=1 --hvx kgdbwait --hvx kgdboc=ttyS1,115200
or at runtime with:
  echo ttyS1,115200 > /sys/module/kgdboc/parameters/kgdboc
  echo g > /proc/sysrq-trigger
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/Kconfig

@@ -127,6 +127,7 @@ config TILEGX
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
+	select HAVE_ARCH_KGDB
 
 config TILEPRO
 	def_bool !TILEGX

arch/tile/include/asm/kgdb.h

+/*
+ * Copyright 2013 Tilera Corporation. All Rights Reserved.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful, but
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ *   NON INFRINGEMENT.  See the GNU General Public License for
+ *   more details.
+ *
+ * TILE-Gx KGDB support.
+ */
+
+#ifndef __TILE_KGDB_H__
+#define __TILE_KGDB_H__
+
+#include <linux/kdebug.h>
+#include <arch/opcode.h>
+
+#define GDB_SIZEOF_REG		sizeof(unsigned long)
+
+/*
+ * TILE-Gx gdb is expecting the following register layout:
+ * 56 GPRs(R0 - R52, TP, SP, LR), 8 special GPRs(networks and ZERO),
+ * plus the PC and the faultnum.
+ *
+ * Even though kernel not use the 8 special GPRs, they need to be present
+ * in the registers sent for correct processing in the host-side gdb.
+ *
+ */
+#define DBG_MAX_REG_NUM		(56+8+2)
+#define NUMREGBYTES		(DBG_MAX_REG_NUM * GDB_SIZEOF_REG)
+
+/*
+ * BUFMAX defines the maximum number of characters in inbound/outbound
+ * buffers at least NUMREGBYTES*2 are needed for register packets,
+ * Longer buffer is needed to list all threads.
+ */
+#define BUFMAX			2048
+
+#define BREAK_INSTR_SIZE	TILEGX_BUNDLE_SIZE_IN_BYTES
+
+/*
+ * Require cache flush for set/clear a software breakpoint or write memory.
+ */
+#define CACHE_FLUSH_IS_SAFE	1
+
+/*
+ * The compiled-in breakpoint instruction can be used to "break" into
+ * the debugger via magic system request key (sysrq-G).
+ */
+static tile_bundle_bits compiled_bpt = TILEGX_BPT_BUNDLE | DIE_COMPILED_BPT;
+
+enum tilegx_regnum {
+	TILEGX_PC_REGNUM = TREG_LAST_GPR + 9,
+	TILEGX_FAULTNUM_REGNUM,
+};
+
+/*
+ * Generate a breakpoint exception to "break" into the debugger.
+ */
+static inline void arch_kgdb_breakpoint(void)
+{
+	asm volatile (".quad %0\n\t"
+		      ::""(compiled_bpt));
+}
+
+#endif /* __TILE_KGDB_H__ */

arch/tile/kernel/Makefile

@@ -29,5 +29,6 @@ obj-$(CONFIG_TILE_USB)		+= usb.o
 obj-$(CONFIG_TILE_HVGLUE_TRACE)	+= hvglue_trace.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= ftrace.o mcount_64.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
+obj-$(CONFIG_KGDB)		+= kgdb.o
 
 obj-y				+= vdso/

arch/tile/kernel/traps.c

@@ -240,6 +240,11 @@ static int do_bpt(struct pt_regs *regs)
 		notify_die(DIE_BREAK, "debug", regs, bundle,
 			INT_ILL, SIGTRAP);
 		break;
+	/* compiled_bpt */
+	case DIE_COMPILED_BPT:
+		notify_die(DIE_COMPILED_BPT, "debug", regs, bundle,
+			INT_ILL, SIGTRAP);
+		break;
 	/* breakpoint2_insn */
 	case DIE_SSTEPBP:
 		notify_die(DIE_SSTEPBP, "single_step", regs, bundle,