s390/early: Dump register contents and call trace for early crashes

If the early program check handler cannot resolve a program check dump
register contents and a call trace to the console before loading a disabled
wait psw. This makes debugging much easier.

Emit an extra message with early_printk() for cases where regular printk()
via the early console is not yet working so that at least some information
is available.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/setup.h

@@ -115,6 +115,8 @@ extern unsigned int console_irq;
 #define SET_CONSOLE_VT220	do { console_mode = 4; } while (0)
 #define SET_CONSOLE_HVC		do { console_mode = 5; } while (0)
 
+void register_early_console(void);
+
 #ifdef CONFIG_VMCP
 void vmcp_cma_reserve(void);
 #else

arch/s390/kernel/early.c

@@ -7,6 +7,7 @@
 #define KMSG_COMPONENT "setup"
 #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
 
+#include <linux/sched/debug.h>
 #include <linux/compiler.h>
 #include <linux/init.h>
 #include <linux/errno.h>
@@ -191,6 +192,15 @@ void __init __do_early_pgm_check(struct pt_regs *regs)
 	}
 	if (fixup_exception(regs))
 		return;
+	/*
+	 * Unhandled exception - system cannot continue but try to get some
+	 * helpful messages to the console. Use early_printk() to print
+	 * some basic information in case it is too early for printk().
+	 */
+	register_early_console();
+	early_printk("PANIC: early exception %04x PSW: %016lx %016lx\n",
+		     regs->int_code & 0xffff, regs->psw.mask, regs->psw.addr);
+	show_regs(regs);
 	disabled_wait();
 }
 

arch/s390/kernel/early_printk.c

@@ -6,6 +6,7 @@
 #include <linux/console.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <asm/setup.h>
 #include <asm/sclp.h>
 
 static void sclp_early_write(struct console *con, const char *s, unsigned int len)
@@ -20,6 +21,16 @@ static struct console sclp_early_console = {
 	.index = -1,
 };
 
+void __init register_early_console(void)
+{
+	if (early_console)
+		return;
+	if (!sclp.has_linemode && !sclp.has_vt220)
+		return;
+	early_console = &sclp_early_console;
+	register_console(early_console);
+}
+
 static int __init setup_early_printk(char *buf)
 {
 	if (early_console)
@@ -27,10 +38,7 @@ static int __init setup_early_printk(char *buf)
 	/* Accept only "earlyprintk" and "earlyprintk=sclp" */
 	if (buf && !str_has_prefix(buf, "sclp"))
 		return 0;
-	if (!sclp.has_linemode && !sclp.has_vt220)
-		return 0;
-	early_console = &sclp_early_console;
-	register_console(early_console);
+	register_early_console();
 	return 0;
 }
 early_param("earlyprintk", setup_early_printk);