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/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;
+}