xen: use the hvc console infrastructure for Xen console

Implement a Xen back-end for hvc console.

* * *
Add early printk support via hvc console, enable using
"earlyprintk=xen" on the kernel command line.

From: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Olof Johansson <olof@lixom.net>

3 files changed, 168 insertions, 0 deletions

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 97bd71bc3aea..9e8f21410d2d 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -604,6 +604,14 @@ config HVC_BEAT
         help
           Toshiba's Cell Reference Set Beat Console device driver
 
+config HVC_XEN
+        bool "Xen Hypervisor Console support"
+        depends on XEN
+        select HVC_DRIVER
+        default y
+        help
+          Xen virtual console device driver
+
 config HVCS
         tristate "IBM Hypervisor Virtual Console Server support"
         depends on PPC_PSERIES
diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index f2996a95eb07..8852b8d643cf 100644
--- a/drivers/char/Makefile
+++ b/drivers/char/Makefile
@@ -48,6 +48,7 @@ obj-$(CONFIG_HVC_ISERIES)	+= hvc_iseries.o
 obj-$(CONFIG_HVC_RTAS)          += hvc_rtas.o
 obj-$(CONFIG_HVC_BEAT)          += hvc_beat.o
 obj-$(CONFIG_HVC_DRIVER)        += hvc_console.o
+obj-$(CONFIG_HVC_XEN)           += hvc_xen.o
 obj-$(CONFIG_RAW_DRIVER)        += raw.o
 obj-$(CONFIG_SGI_SNSC)          += snsc.o snsc_event.o
 obj-$(CONFIG_MSPEC)             += mspec.o
diff --git a/drivers/char/hvc_xen.c b/drivers/char/hvc_xen.c
new file mode 100644
index 000000000000..dd68f8541c2d
--- /dev/null
+++ b/drivers/char/hvc_xen.c
@@ -0,0 +1,159 @@
+/*
+ * xen console driver interface to hvc_console.c
+ *
+ * (c) 2007 Gerd Hoffmann <kraxel@suse.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
+ */
+
+#include <linux/console.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/types.h>
+
+#include <asm/xen/hypervisor.h>
+#include <xen/page.h>
+#include <xen/events.h>
+#include <xen/interface/io/console.h>
+#include <xen/hvc-console.h>
+
+#include "hvc_console.h"
+
+#define HVC_COOKIE   0x58656e /* "Xen" in hex */
+
+static struct hvc_struct *hvc;
+static int xencons_irq;
+
+/* ------------------------------------------------------------------ */
+
+static inline struct xencons_interface *xencons_interface(void)
+{
+        return mfn_to_virt(xen_start_info->console.domU.mfn);
+}
+
+static inline void notify_daemon(void)
+{
+        /* Use evtchn: this is called early, before irq is set up. */
+        notify_remote_via_evtchn(xen_start_info->console.domU.evtchn);
+}
+
+static int write_console(uint32_t vtermno, const char *data, int len)
+{
+        struct xencons_interface *intf = xencons_interface();
+        XENCONS_RING_IDX cons, prod;
+        int sent = 0;
+
+        cons = intf->out_cons;
+        prod = intf->out_prod;
+        mb();                   /* update queue values before going on */
+        BUG_ON((prod - cons) > sizeof(intf->out));
+
+        while ((sent < len) && ((prod - cons) < sizeof(intf->out)))
+                intf->out[MASK_XENCONS_IDX(prod++, intf->out)] = data[sent++];
+
+        wmb();                  /* write ring before updating pointer */
+        intf->out_prod = prod;
+
+        notify_daemon();
+        return sent;
+}
+
+static int read_console(uint32_t vtermno, char *buf, int len)
+{
+        struct xencons_interface *intf = xencons_interface();
+        XENCONS_RING_IDX cons, prod;
+        int recv = 0;
+
+        cons = intf->in_cons;
+        prod = intf->in_prod;
+        mb();                   /* get pointers before reading ring */
+        BUG_ON((prod - cons) > sizeof(intf->in));
+
+        while (cons != prod && recv < len)
+                buf[recv++] = intf->in[MASK_XENCONS_IDX(cons++, intf->in)];
+
+        mb();                   /* read ring before consuming */
+        intf->in_cons = cons;
+
+        notify_daemon();
+        return recv;
+}
+
+static struct hv_ops hvc_ops = {
+        .get_chars = read_console,
+        .put_chars = write_console,
+};
+
+static int __init xen_init(void)
+{
+        struct hvc_struct *hp;
+
+        if (!is_running_on_xen())
+                return 0;
+
+        xencons_irq = bind_evtchn_to_irq(xen_start_info->console.domU.evtchn);
+        if (xencons_irq < 0)
+                xencons_irq = 0 /* NO_IRQ */;
+        hp = hvc_alloc(HVC_COOKIE, xencons_irq, &hvc_ops, 256);
+        if (IS_ERR(hp))
+                return PTR_ERR(hp);
+
+        hvc = hp;
+        return 0;
+}
+
+static void __exit xen_fini(void)
+{
+        if (hvc)
+                hvc_remove(hvc);
+}
+
+static int xen_cons_init(void)
+{
+        if (!is_running_on_xen())
+                return 0;
+
+        hvc_instantiate(HVC_COOKIE, 0, &hvc_ops);
+        return 0;
+}
+
+module_init(xen_init);
+module_exit(xen_fini);
+console_initcall(xen_cons_init);
+
+static void xenboot_write_console(struct console *console, const char *string,
+                                  unsigned len)
+{
+        unsigned int linelen, off = 0;
+        const char *pos;
+
+        while (off < len && NULL != (pos = strchr(string+off, '\n'))) {
+                linelen = pos-string+off;
+                if (off + linelen > len)
+                        break;
+                write_console(0, string+off, linelen);
+                write_console(0, "\r\n", 2);
+                off += linelen + 1;
+        }
+        if (off < len)
+                write_console(0, string+off, len-off);
+}
+
+struct console xenboot_console = {
+        .name           = "xenboot",
+        .write          = xenboot_write_console,
+        .flags          = CON_PRINTBUFFER | CON_BOOT,
+};