s390: provide sclp based boot console

Use the early sclp code to provide a boot console. This boot console
is available if the kernel parameter "earlyprintk" has been specified,
just like it works for other architectures that also provide an early
boot console.

This makes debugging of early problems much easier, since now we
finally have working console output even before memory detection is
running.

The boot console will be automatically disabled as soon as another
console will be registered.

Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -979,9 +979,10 @@
 			address. The serial port must already be setup
 			and configured. Options are not yet supported.
 
-	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
+	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k,S390]
 			earlyprintk=vga
 			earlyprintk=efi
+			earlyprintk=sclp
 			earlyprintk=xen
 			earlyprintk=serial[,ttySn[,baudrate]]
 			earlyprintk=serial[,0x...[,baudrate]]
@@ -1016,6 +1017,8 @@
 
 			The xen output can only be used by Xen PV guests.
 
+			The sclp output can only be used on s390.
+
 	edac_report=	[HW,EDAC] Control how to report EDAC event
 			Format: {"on" | "off" | "force"}
 			on: enable EDAC to report H/W event. May be overridden

arch/s390/Kconfig.debug

@@ -20,4 +20,8 @@ config S390_PTDUMP
 config DEBUG_SET_MODULE_RONX
 	def_bool y
 	depends on MODULES
+
+config EARLY_PRINTK
+	def_bool y
+
 endmenu

arch/s390/include/asm/sclp.h

@@ -118,6 +118,7 @@ int memcpy_hsa_kernel(void *dest, unsigned long src, size_t count);
 int memcpy_hsa_user(void __user *dest, unsigned long src, size_t count);
 void sclp_early_detect(void);
 void _sclp_print_early(const char *);
+void __sclp_print_early(const char *s, unsigned int len);
 void sclp_ocf_cpc_name_copy(char *dst);
 
 static inline int sclp_get_core_info(struct sclp_core_info *info, int early)

arch/s390/kernel/Makefile

@@ -76,7 +76,7 @@ obj-$(CONFIG_AUDIT)		+= audit.o
 compat-obj-$(CONFIG_AUDIT)	+= compat_audit.o
 obj-$(CONFIG_COMPAT)		+= compat_linux.o compat_signal.o
 obj-$(CONFIG_COMPAT)		+= compat_wrapper.o $(compat-obj-y)
-
+obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o
 obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o

arch/s390/kernel/early_printk.c

@@ -0,0 +1,35 @@
+/*
+ *    Copyright IBM Corp. 2017
+ */
+
+#include <linux/console.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <asm/sclp.h>
+
+static void sclp_early_write(struct console *con, const char *s, unsigned int len)
+{
+	__sclp_print_early(s, len);
+}
+
+static struct console sclp_early_console = {
+	.name  = "earlysclp",
+	.write = sclp_early_write,
+	.flags = CON_PRINTBUFFER | CON_BOOT,
+	.index = -1,
+};
+
+static int __init setup_early_printk(char *buf)
+{
+	if (early_console)
+		return 0;
+	/* Accept only "earlyprintk" and "earlyprintk=sclp" */
+	if (buf && strncmp(buf, "sclp", 4))
+		return 0;
+	if (!sclp.has_linemode && !sclp.has_vt220)
+		return 0;
+	early_console = &sclp_early_console;
+	register_console(early_console);
+	return 0;
+}
+early_param("earlyprintk", setup_early_printk);

arch/s390/kernel/sclp.c

@@ -98,7 +98,7 @@ static int _sclp_setup(int disable)
 }
 
 /* Output multi-line text using SCLP Message interface. */
-static void _sclp_print_lm(const char *str)
+static void _sclp_print_lm(const char *str, unsigned int len)
 {
 	static unsigned char write_head[] = {
 		/* sccb header */
@@ -133,16 +133,19 @@ static void _sclp_print_lm(const char *str)
 		0x00, 0x00, 0x00, 0x00				/* 6 */
 	};
 	unsigned char *ptr, *end_ptr, ch;
-	unsigned int count;
+	unsigned int count, num;
 
+	num = 0;
 	memcpy(_sclp_work_area, write_head, sizeof(write_head));
 	ptr = _sclp_work_area + sizeof(write_head);
 	end_ptr = _sclp_work_area + sizeof(_sclp_work_area) - 1;
 	do {
 		if (ptr + sizeof(write_mto) > end_ptr)
 			break;
 		memcpy(ptr, write_mto, sizeof(write_mto));
-		for (count = sizeof(write_mto); (ch = *str++) != 0; count++) {
+		for (count = sizeof(write_mto); num < len; count++) {
+			num++;
+			ch = *str++;
 			if (ch == 0x0a)
 				break;
 			if (ptr > end_ptr)
@@ -155,7 +158,7 @@ static void _sclp_print_lm(const char *str)
 		*(unsigned short *)(_sclp_work_area + 8) += count;
 		*(unsigned short *)(_sclp_work_area + 0) += count;
 		ptr += count;
-	} while (ch != 0);
+	} while (num < len);
 
 	/* SCLP write data */
 	_sclp_servc(0x00760005, _sclp_work_area);
@@ -164,7 +167,7 @@ static void _sclp_print_lm(const char *str)
 /* Output multi-line text (plus a newline) using SCLP VT220
  * interface.
  */
-static void _sclp_print_vt220(const char *str)
+static void _sclp_print_vt220(const char *str, unsigned int len)
 {
 	static unsigned char const write_head[] = {
 		/* sccb header */
@@ -174,7 +177,6 @@ static void _sclp_print_vt220(const char *str)
 		0x00, 0x06,
 		0x1a, 0x00, 0x00, 0x00,
 	};
-	size_t len = strlen(str);
 
 	if (sizeof(write_head) + len >= sizeof(_sclp_work_area))
 		len = sizeof(_sclp_work_area) - sizeof(write_head) - 1;
@@ -194,13 +196,18 @@ static void _sclp_print_vt220(const char *str)
 /* Output one or more lines of text on the SCLP console (VT220 and /
  * or line-mode). All lines get terminated; no need for a trailing LF.
  */
-void _sclp_print_early(const char *str)
+void __sclp_print_early(const char *str, unsigned int len)
 {
 	if (_sclp_setup(0) != 0)
 		return;
 	if (have_linemode)
-		_sclp_print_lm(str);
+		_sclp_print_lm(str, len);
 	if (have_vt220)
-		_sclp_print_vt220(str);
+		_sclp_print_vt220(str, len);
 	_sclp_setup(1);
 }
+
+void _sclp_print_early(const char *str)
+{
+	__sclp_print_early(str, strlen(str));
+}