powerpc/83xx: handle machine check caused by watchdog timer

When the watchdog timer is set in interrupt mode, it causes a
machine check when it times out. The purpose of this mode is to
ease debugging, not to crash the kernel and reboot the machine.

This patch implements a special handling for that, in order to not
crash the kernel if the watchdog times out while in interrupt or
within the idle task.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[scottwood: added missing #include]
Signed-off-by: Scott Wood <oss@buserror.net>

arch/powerpc/include/asm/cputable.h

@@ -44,6 +44,7 @@ extern int machine_check_e500(struct pt_regs *regs);
 extern int machine_check_e200(struct pt_regs *regs);
 extern int machine_check_47x(struct pt_regs *regs);
 int machine_check_8xx(struct pt_regs *regs);
+int machine_check_83xx(struct pt_regs *regs);
 
 extern void cpu_down_flush_e500v2(void);
 extern void cpu_down_flush_e500mc(void);

arch/powerpc/include/asm/reg.h

@@ -769,6 +769,8 @@
 #define   SRR1_PROGTRAP		0x00020000 /* Trap */
 #define   SRR1_PROGADDR		0x00010000 /* SRR0 contains subsequent addr */
 
+#define   SRR1_MCE_MCP		0x00080000 /* Machine check signal caused interrupt */
+
 #define SPRN_HSRR0	0x13A	/* Save/Restore Register 0 */
 #define SPRN_HSRR1	0x13B	/* Save/Restore Register 1 */
 #define   HSRR1_DENORM		0x00100000 /* Denorm exception */

arch/powerpc/kernel/cputable.c

@@ -1141,6 +1141,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.machine_check		= machine_check_generic,
 		.platform		= "ppc603",
 	},
+#ifdef CONFIG_PPC_83xx
 	{	/* e300c1 (a 603e core, plus some) on 83xx */
 		.pvr_mask		= 0x7fff0000,
 		.pvr_value		= 0x00830000,
@@ -1151,7 +1152,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.icache_bsize		= 32,
 		.dcache_bsize		= 32,
 		.cpu_setup		= __setup_cpu_603,
-		.machine_check		= machine_check_generic,
+		.machine_check		= machine_check_83xx,
 		.platform		= "ppc603",
 	},
 	{	/* e300c2 (an e300c1 core, plus some, minus FPU) on 83xx */
@@ -1165,7 +1166,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.icache_bsize		= 32,
 		.dcache_bsize		= 32,
 		.cpu_setup		= __setup_cpu_603,
-		.machine_check		= machine_check_generic,
+		.machine_check		= machine_check_83xx,
 		.platform		= "ppc603",
 	},
 	{	/* e300c3 (e300c1, plus one IU, half cache size) on 83xx */
@@ -1179,7 +1180,7 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.icache_bsize		= 32,
 		.dcache_bsize		= 32,
 		.cpu_setup		= __setup_cpu_603,
-		.machine_check		= machine_check_generic,
+		.machine_check		= machine_check_83xx,
 		.num_pmcs		= 4,
 		.oprofile_cpu_type	= "ppc/e300",
 		.oprofile_type		= PPC_OPROFILE_FSL_EMB,
@@ -1196,12 +1197,13 @@ static struct cpu_spec __initdata cpu_specs[] = {
 		.icache_bsize		= 32,
 		.dcache_bsize		= 32,
 		.cpu_setup		= __setup_cpu_603,
-		.machine_check		= machine_check_generic,
+		.machine_check		= machine_check_83xx,
 		.num_pmcs		= 4,
 		.oprofile_cpu_type	= "ppc/e300",
 		.oprofile_type		= PPC_OPROFILE_FSL_EMB,
 		.platform		= "ppc603",
 	},
+#endif
 	{	/* default match, we assume split I/D cache & TB (non-601)... */
 		.pvr_mask		= 0x00000000,
 		.pvr_value		= 0x00000000,

arch/powerpc/platforms/83xx/misc.c

@@ -14,6 +14,7 @@
 #include <linux/of_platform.h>
 #include <linux/pci.h>
 
+#include <asm/debug.h>
 #include <asm/io.h>
 #include <asm/hw_irq.h>
 #include <asm/ipic.h>
@@ -150,3 +151,19 @@ void __init mpc83xx_setup_arch(void)
 
 	mpc83xx_setup_pci();
 }
+
+int machine_check_83xx(struct pt_regs *regs)
+{
+	u32 mask = 1 << (31 - IPIC_MCP_WDT);
+
+	if (!(regs->msr & SRR1_MCE_MCP) || !(ipic_get_mcp_status() & mask))
+		return machine_check_generic(regs);
+	ipic_clear_mcp_status(mask);
+
+	if (debugger_fault_handler(regs))
+		return 1;
+
+	die("Watchdog NMI Reset", regs, 0);
+
+	return 1;
+}