s390: use virtio_console for KVM on s390

This patch enables virtio_console as the default console on kvm for
s390. We currently use the same notify hack as lguest for early
console output. I will try to address this for lguest and s390 later.

Signed-off-by: Christian Borntraeger <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

arch/s390/Kconfig

···
 	depends on 64BIT && EXPERIMENTAL
 	select VIRTIO
 	select VIRTIO_RING
+	select VIRTIO_CONSOLE
 	help
 	  Select this option if you want to run the kernel under s390 linux
 endmenu

arch/s390/kernel/setup.c

···
 #include <asm/sections.h>
 #include <asm/ebcdic.h>
 #include <asm/compat.h>
+#include <asm/kvm_virtio.h>
 
 long psw_kernel_bits	= (PSW_BASE_BITS | PSW_MASK_DAT | PSW_ASC_PRIMARY |
 			   PSW_MASK_MCHECK | PSW_DEFAULT_KEY);
···
 		printk("We are running under VM (64 bit mode)\n");
 	else if (MACHINE_IS_KVM) {
 		printk("We are running under KVM (64 bit mode)\n");
-		add_preferred_console("ttyS", 1, NULL);
+		add_preferred_console("hvc", 0, NULL);
+		s390_virtio_console_init();
 	} else
 		printk("We are running native (64 bit mode)\n");
 #endif /* CONFIG_64BIT */

drivers/s390/kvm/kvm_virtio.c

···
 #include <linux/err.h>
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
+#include <linux/virtio_console.h>
 #include <linux/interrupt.h>
 #include <linux/virtio_ring.h>
 #include <linux/pfn.h>
···
 
 	scan_devices();
 	return 0;
+}
+
+/* code for early console output with virtio_console */
+static __init int early_put_chars(u32 vtermno, const char *buf, int count)
+{
+	char scratch[17];
+	unsigned int len = count;
+
+	if (len > sizeof(scratch) - 1)
+		len = sizeof(scratch) - 1;
+	scratch[len] = '\0';
+	memcpy(scratch, buf, len);
+	kvm_hypercall1(KVM_S390_VIRTIO_NOTIFY, __pa(scratch));
+	return len;
+}
+
+void s390_virtio_console_init(void)
+{
+	virtio_cons_early_init(early_put_chars);
 }
 
 /*

include/asm-s390/kvm_virtio.h

···
 #define KVM_S390_VIRTIO_RESET		1
 #define KVM_S390_VIRTIO_SET_STATUS	2
 
+#ifdef __KERNEL__
+/* early virtio console setup */
+#ifdef CONFIG_VIRTIO_CONSOLE
+extern void s390_virtio_console_init(void);
+#else
+static inline void s390_virtio_console_init(void)
+{
+}
+#endif /* CONFIG_VIRTIO_CONSOLE */
+#endif /* __KERNEL__ */
 #endif