MIPS: add handling for generic and EJTAG exceptions

Add exception handlers for generic and EJTAG exceptions. Most of
the assembly code is imported from Linux kernel and adapted to U-Boot.
The exception vector table will be reserved above the stack before
U-Boot is relocated. The exception handlers will be installed and
activated after relocation in the initr_traps hook function.

Generic exceptions are handled by showing a CPU register dump similar
to Linux kernel. For example:

malta # md 1
00000001:
Ooops:
$ 0   : 00000000 00000000 00000009 00000004
$ 4   : 8ff7e108 00000000 0000003a 00000000
$ 8   : 00000008 00000001 8ff7cd18 00000004
$12   : 00000002 00000000 00000005 0000003a
$16   : 00000004 00000040 00000001 00000001
$20   : 00000000 8fff53c0 00000008 00000004
$24   : ffffffff 8ffdea44
$28   : 90001650 8ff7cd00 00000004 8ffe6818
Hi    : 00000000
Lo    : 00000004
epc   : 8ffe6848 (text bfc28848)
ra    : 8ffe6818 (text bfc28818)
Status: 00000006
Cause : 00000410 (ExcCode 04)
BadVA : 8ff9e928
PrId  : 00019300
 ### ERROR ### Please RESET the board ###

EJTAG exceptions are checked for SDBBP and delegated to the SDBBP handler
if necessary. Otherwise the debug mode will simply be exited. The SDBBP
handler currently prints the contents of registers c0_depc and c0_debug.
This could be extended in the future to handle semi-hosting according to
the MIPS UHI specification.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Tested-by: Paul Burton <paul.burton@imgtec.com>

1 files changed, 106 insertions, 0 deletions

diff --git a/arch/mips/lib/traps.c b/arch/mips/lib/traps.c
new file mode 100644
index 0000000000..18622c223d
--- /dev/null
+++ b/arch/mips/lib/traps.c
@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 1994 - 1999, 2000, 01, 06 Ralf Baechle
+ * Copyright (C) 1995, 1996 Paul M. Antoine
+ * Copyright (C) 1998 Ulf Carlsson
+ * Copyright (C) 1999 Silicon Graphics, Inc.
+ * Kevin D. Kissell, kevink@mips.com and Carsten Langgaard, carstenl@mips.com
+ * Copyright (C) 2002, 2003, 2004, 2005, 2007  Maciej W. Rozycki
+ * Copyright (C) 2000, 2001, 2012 MIPS Technologies, Inc.  All rights reserved.
+ * Copyright (C) 2014, Imagination Technologies Ltd.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <asm/mipsregs.h>
+#include <asm/addrspace.h>
+#include <asm/system.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+static void show_regs(const struct pt_regs *regs)
+{
+	const int field = 2 * sizeof(unsigned long);
+	unsigned int cause = regs->cp0_cause;
+	unsigned int exccode;
+	int i;
+
+	/*
+	 * Saved main processor registers
+	 */
+	for (i = 0; i < 32; ) {
+		if ((i % 4) == 0)
+			printf("$%2d   :", i);
+		if (i == 0)
+			printf(" %0*lx", field, 0UL);
+		else if (i == 26 || i == 27)
+			printf(" %*s", field, "");
+		else
+			printf(" %0*lx", field, regs->regs[i]);
+
+		i++;
+		if ((i % 4) == 0)
+			puts("\n");
+	}
+
+	printf("Hi    : %0*lx\n", field, regs->hi);
+	printf("Lo    : %0*lx\n", field, regs->lo);
+
+	/*
+	 * Saved cp0 registers
+	 */
+	printf("epc   : %0*lx (text %0*lx)\n", field, regs->cp0_epc,
+	       field, regs->cp0_epc - gd->reloc_off);
+	printf("ra    : %0*lx (text %0*lx)\n", field, regs->regs[31],
+	       field, regs->regs[31] - gd->reloc_off);
+
+	printf("Status: %08x\n", (uint32_t) regs->cp0_status);
+
+	exccode = (cause & CAUSEF_EXCCODE) >> CAUSEB_EXCCODE;
+	printf("Cause : %08x (ExcCode %02x)\n", cause, exccode);
+
+	if (1 <= exccode && exccode <= 5)
+		printf("BadVA : %0*lx\n", field, regs->cp0_badvaddr);
+
+	printf("PrId  : %08x\n", read_c0_prid());
+}
+
+void do_reserved(const struct pt_regs *regs)
+{
+	puts("\nOoops:\n");
+	show_regs(regs);
+	hang();
+}
+
+void do_ejtag_debug(const struct pt_regs *regs)
+{
+	const int field = 2 * sizeof(unsigned long);
+	unsigned long depc;
+	unsigned int debug;
+
+	depc = read_c0_depc();
+	debug = read_c0_debug();
+
+	printf("SDBBP EJTAG debug exception: c0_depc = %0*lx, DEBUG = %08x\n",
+	       field, depc, debug);
+}
+
+static void set_handler(unsigned long offset, void *addr, unsigned long size)
+{
+	unsigned long ebase = gd->irq_sp;
+
+	memcpy((void *)(ebase + offset), addr, size);
+	flush_cache(ebase + offset, size);
+}
+
+void trap_init(ulong reloc_addr)
+{
+	unsigned long ebase = gd->irq_sp;
+
+	set_handler(0x180, &except_vec3_generic, 0x80);
+	set_handler(0x280, &except_vec_ejtag_debug, 0x80);
+
+	write_c0_ebase(ebase);
+	clear_c0_status(ST0_BEV);
+	execution_hazard_barrier();
+}