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/include/asm/kgdb.h

@@ -0,0 +1,71 @@
+/*
+ * 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__ */