hvc_console: rework setup to replace irq functions with callbacks

This patch tries to change hvc_console to not use request_irq/free_irq if
the backend does not use irqs. This allows virtio_console to use hvc_console
without having a linker reference to request_irq/free_irq.

In addition, together with patch 2/3 it improves the performance for virtio
console input. (an earlier version of this patch was tested by Yajin on lguest)

The irq specific code is moved to hvc_irq.c and selected by the drivers that
use irqs (System p, System i, XEN).

I replaced "int irq" with the opaque "int data". The request_irq and
free_irq calls are replaced with notifier_add and notifier_del. I have also
changed the code a bit to call the notifier_add and notifier_del inside the
spinlock area as the callbacks are found via hp->ops.

Changes since last version:
o remove ifdef
o reintroduce "irq_requested" as "notified"
o cleanups, sparse..

I did not move the timer based polling into a separate polling scheme. I
played with several variants, but it seems we need to sleep/schedule in
a thread even for irq based consoles, as there are throttleing and buffer
size constraints.

I also kept hvc_struct defined in hvc_console.h so that hvc_irq.c can access
the irq_requested element.

Feedback is appreciated. virtio_console is currently the only available console
for kvm on s390. I plan to push this change as soon as all affected parties
agree on it. I would love to get test results from System p, Xen etc.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

8 files changed, 105 insertions, 67 deletions

diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 67b07576f8bf..d825361a6baf 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -578,11 +578,14 @@ config HVC_DRIVER
           It will automatically be selected if one of the back-end console drivers
           is selected.
 
+config HVC_IRQ
+        bool
 
 config HVC_CONSOLE
         bool "pSeries Hypervisor Virtual Console support"
         depends on PPC_PSERIES
         select HVC_DRIVER
+        select HVC_IRQ
         help
           pSeries machines when partitioned support a hypervisor virtual
           console. This driver allows each pSeries partition to have a console
@@ -593,6 +596,7 @@ config HVC_ISERIES
         depends on PPC_ISERIES
         default y
         select HVC_DRIVER
+        select HVC_IRQ
         help
           iSeries machines support a hypervisor virtual console.
 
@@ -614,6 +618,7 @@ config HVC_XEN
         bool "Xen Hypervisor Console support"
         depends on XEN
         select HVC_DRIVER
+        select HVC_IRQ
         default y
         help
           Xen virtual console device driver
diff --git a/drivers/char/Makefile b/drivers/char/Makefile
index 4b6e736cfa02..eb02c3506800 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-$(CONFIG_HVC_IRQ)           += hvc_irq.o
 obj-$(CONFIG_HVC_XEN)           += hvc_xen.o
 obj-$(CONFIG_VIRTIO_CONSOLE)    += virtio_console.o
 obj-$(CONFIG_RAW_DRIVER)        += raw.o
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 2f9759d625cc..2f5b7fb67045 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -27,7 +27,6 @@
 #include <linux/init.h>
 #include <linux/kbd_kern.h>
 #include <linux/kernel.h>
-#include <linux/kref.h>
 #include <linux/kthread.h>
 #include <linux/list.h>
 #include <linux/module.h>
@@ -75,23 +74,6 @@ static int hvc_init(void);
 static int sysrq_pressed;
 #endif
 
-struct hvc_struct {
-        spinlock_t lock;
-        int index;
-        struct tty_struct *tty;
-        unsigned int count;
-        int do_wakeup;
-        char *outbuf;
-        int outbuf_size;
-        int n_outbuf;
-        uint32_t vtermno;
-        struct hv_ops *ops;
-        int irq_requested;
-        int irq;
-        struct list_head next;
-        struct kref kref; /* ref count & hvc_struct lifetime */
-};
-
 /* dynamic list of hvc_struct instances */
 static LIST_HEAD(hvc_structs);
 
@@ -300,26 +282,12 @@ int hvc_instantiate(uint32_t vtermno, int index, struct hv_ops *ops)
 }
 
 /* Wake the sleeping khvcd */
-static void hvc_kick(void)
+void hvc_kick(void)
 {
         hvc_kicked = 1;
         wake_up_process(hvc_task);
 }
 
-static int hvc_poll(struct hvc_struct *hp);
-
-/*
- * NOTE: This API isn't used if the console adapter doesn't support interrupts.
- * In this case the console is poll driven.
- */
-static irqreturn_t hvc_handle_interrupt(int irq, void *dev_instance)
-{
-        /* if hvc_poll request a repoll, then kick the hvcd thread */
-        if (hvc_poll(dev_instance))
-                hvc_kick();
-        return IRQ_HANDLED;
-}
-
 static void hvc_unthrottle(struct tty_struct *tty)
 {
         hvc_kick();
@@ -333,7 +301,6 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
 {
         struct hvc_struct *hp;
         unsigned long flags;
-        int irq = 0;
         int rc = 0;
 
         /* Auto increments kref reference if found. */
@@ -352,18 +319,15 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
         tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */
 
         hp->tty = tty;
-        /* Save for request_irq outside of spin_lock. */
-        irq = hp->irq;
-        if (irq)
-                hp->irq_requested = 1;
+
+        if (hp->ops->notifier_add)
+                rc = hp->ops->notifier_add(hp, hp->data);
 
         spin_unlock_irqrestore(&hp->lock, flags);
-        /* check error, fallback to non-irq */
-        if (irq)
-                rc = request_irq(irq, hvc_handle_interrupt, IRQF_DISABLED, "hvc_console", hp);
+
 
         /*
-         * If the request_irq() fails and we return an error.  The tty layer
+         * If the notifier fails we return an error.  The tty layer
          * will call hvc_close() after a failed open but we don't want to clean
          * up there so we'll clean up here and clear out the previously set
          * tty fields and return the kref reference.
@@ -371,7 +335,6 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
         if (rc) {
                 spin_lock_irqsave(&hp->lock, flags);
                 hp->tty = NULL;
-                hp->irq_requested = 0;
                 spin_unlock_irqrestore(&hp->lock, flags);
                 tty->driver_data = NULL;
                 kref_put(&hp->kref, destroy_hvc_struct);
@@ -386,7 +349,6 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
 static void hvc_close(struct tty_struct *tty, struct file * filp)
 {
         struct hvc_struct *hp;
-        int irq = 0;
         unsigned long flags;
 
         if (tty_hung_up_p(filp))
@@ -404,9 +366,8 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
         spin_lock_irqsave(&hp->lock, flags);
 
         if (--hp->count == 0) {
-                if (hp->irq_requested)
-                        irq = hp->irq;
-                hp->irq_requested = 0;
+                if (hp->ops->notifier_del)
+                        hp->ops->notifier_del(hp, hp->data);
 
                 /* We are done with the tty pointer now. */
                 hp->tty = NULL;
@@ -418,10 +379,6 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
                  * waking periodically to check chars_in_buffer().
                  */
                 tty_wait_until_sent(tty, HVC_CLOSE_WAIT);
-
-                if (irq)
-                        free_irq(irq, hp);
-
         } else {
                 if (hp->count < 0)
                         printk(KERN_ERR "hvc_close %X: oops, count is %d\n",
@@ -436,7 +393,6 @@ static void hvc_hangup(struct tty_struct *tty)
 {
         struct hvc_struct *hp = tty->driver_data;
         unsigned long flags;
-        int irq = 0;
         int temp_open_count;
 
         if (!hp)
@@ -458,13 +414,12 @@ static void hvc_hangup(struct tty_struct *tty)
         hp->count = 0;
         hp->n_outbuf = 0;
         hp->tty = NULL;
-        if (hp->irq_requested)
-                /* Saved for use outside of spin_lock. */
-                irq = hp->irq;
-        hp->irq_requested = 0;
+
+        if (hp->ops->notifier_del)
+                        hp->ops->notifier_del(hp, hp->data);
+
         spin_unlock_irqrestore(&hp->lock, flags);
-        if (irq)
-                free_irq(irq, hp);
+
         while(temp_open_count) {
                 --temp_open_count;
                 kref_put(&hp->kref, destroy_hvc_struct);
@@ -575,7 +530,7 @@ static u32 timeout = MIN_TIMEOUT;
 #define HVC_POLL_READ   0x00000001
 #define HVC_POLL_WRITE  0x00000002
 
-static int hvc_poll(struct hvc_struct *hp)
+int hvc_poll(struct hvc_struct *hp)
 {
         struct tty_struct *tty;
         int i, n, poll_mask = 0;
@@ -602,10 +557,10 @@ static int hvc_poll(struct hvc_struct *hp)
         if (test_bit(TTY_THROTTLED, &tty->flags))
                 goto throttled;
 
-        /* If we aren't interrupt driven and aren't throttled, we always
+        /* If we aren't notifier driven and aren't throttled, we always
          * request a reschedule
          */
-        if (hp->irq == 0)
+        if (!hp->irq_requested)
                 poll_mask |= HVC_POLL_READ;
 
         /* Read data if any */
@@ -733,7 +688,7 @@ static const struct tty_operations hvc_ops = {
         .chars_in_buffer = hvc_chars_in_buffer,
 };
 
-struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int irq,
+struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int data,
                                         struct hv_ops *ops, int outbuf_size)
 {
         struct hvc_struct *hp;
@@ -754,7 +709,7 @@ struct hvc_struct __devinit *hvc_alloc(uint32_t vtermno, int irq,
         memset(hp, 0x00, sizeof(*hp));
 
         hp->vtermno = vtermno;
-        hp->irq = irq;
+        hp->data = data;
         hp->ops = ops;
         hp->outbuf_size = outbuf_size;
         hp->outbuf = &((char *)hp)[ALIGN(sizeof(*hp), sizeof(long))];
diff --git a/drivers/char/hvc_console.h b/drivers/char/hvc_console.h
index 42ffb17e15df..d9ce10915625 100644
--- a/drivers/char/hvc_console.h
+++ b/drivers/char/hvc_console.h
@@ -26,6 +26,7 @@
 
 #ifndef HVC_CONSOLE_H
 #define HVC_CONSOLE_H
+#include <linux/kref.h>
 
 /*
  * This is the max number of console adapters that can/will be found as
@@ -42,24 +43,50 @@
  */
 #define HVC_ALLOC_TTY_ADAPTERS  8
 
+struct hvc_struct {
+        spinlock_t lock;
+        int index;
+        struct tty_struct *tty;
+        unsigned int count;
+        int do_wakeup;
+        char *outbuf;
+        int outbuf_size;
+        int n_outbuf;
+        uint32_t vtermno;
+        struct hv_ops *ops;
+        int irq_requested;
+        int data;
+        struct list_head next;
+        struct kref kref; /* ref count & hvc_struct lifetime */
+};
 
 /* implemented by a low level driver */
 struct hv_ops {
         int (*get_chars)(uint32_t vtermno, char *buf, int count);
         int (*put_chars)(uint32_t vtermno, const char *buf, int count);
-};
 
-struct hvc_struct;
+        /* Callbacks for notification. Called in open and close */
+        int (*notifier_add)(struct hvc_struct *hp, int irq);
+        void (*notifier_del)(struct hvc_struct *hp, int irq);
+};
 
 /* Register a vterm and a slot index for use as a console (console_init) */
 extern int hvc_instantiate(uint32_t vtermno, int index, struct hv_ops *ops);
 
 /* register a vterm for hvc tty operation (module_init or hotplug add) */
-extern struct hvc_struct * __devinit hvc_alloc(uint32_t vtermno, int irq,
+extern struct hvc_struct * __devinit hvc_alloc(uint32_t vtermno, int data,
                                 struct hv_ops *ops, int outbuf_size);
-/* remove a vterm from hvc tty operation (modele_exit or hotplug remove) */
+/* remove a vterm from hvc tty operation (module_exit or hotplug remove) */
 extern int __devexit hvc_remove(struct hvc_struct *hp);
 
+/* data available */
+int hvc_poll(struct hvc_struct *hp);
+void hvc_kick(void);
+
+/* default notifier for irq based notification */
+extern int notifier_add_irq(struct hvc_struct *hp, int data);
+extern void notifier_del_irq(struct hvc_struct *hp, int data);
+
 
 #if defined(CONFIG_XMON) && defined(CONFIG_SMP)
 #include <asm/xmon.h>
diff --git a/drivers/char/hvc_irq.c b/drivers/char/hvc_irq.c
new file mode 100644
index 000000000000..73a59cdb8947
--- /dev/null
+++ b/drivers/char/hvc_irq.c
@@ -0,0 +1,44 @@
+/*
+ * Copyright IBM Corp. 2001,2008
+ *
+ * This file contains the IRQ specific code for hvc_console
+ *
+ */
+
+#include <linux/interrupt.h>
+
+#include "hvc_console.h"
+
+static irqreturn_t hvc_handle_interrupt(int irq, void *dev_instance)
+{
+        /* if hvc_poll request a repoll, then kick the hvcd thread */
+        if (hvc_poll(dev_instance))
+                hvc_kick();
+        return IRQ_HANDLED;
+}
+
+/*
+ * For IRQ based systems these callbacks can be used
+ */
+int notifier_add_irq(struct hvc_struct *hp, int irq)
+{
+        int rc;
+
+        if (!irq) {
+                hp->irq_requested = 0;
+                return 0;
+        }
+        rc = request_irq(irq, hvc_handle_interrupt, IRQF_DISABLED,
+                           "hvc_console", hp);
+        if (!rc)
+                hp->irq_requested = 1;
+        return rc;
+}
+
+void notifier_del_irq(struct hvc_struct *hp, int irq)
+{
+        if (!irq)
+                return;
+        free_irq(irq, hp);
+        hp->irq_requested = 0;
+}
diff --git a/drivers/char/hvc_iseries.c b/drivers/char/hvc_iseries.c
index a08f8f981c11..b71c610fe5ae 100644
--- a/drivers/char/hvc_iseries.c
+++ b/drivers/char/hvc_iseries.c
@@ -200,6 +200,8 @@ done:
 static struct hv_ops hvc_get_put_ops = {
         .get_chars = get_chars,
         .put_chars = put_chars,
+        .notifier_add = notifier_add_irq,
+        .notifier_del = notifier_del_irq,
 };
 
 static int __devinit hvc_vio_probe(struct vio_dev *vdev,
diff --git a/drivers/char/hvc_vio.c b/drivers/char/hvc_vio.c
index 79711aa4b41d..93f3840c1682 100644
--- a/drivers/char/hvc_vio.c
+++ b/drivers/char/hvc_vio.c
@@ -80,6 +80,8 @@ static int filtered_get_chars(uint32_t vtermno, char *buf, int count)
 static struct hv_ops hvc_get_put_ops = {
         .get_chars = filtered_get_chars,
         .put_chars = hvc_put_chars,
+        .notifier_add = notifier_add_irq,
+        .notifier_del = notifier_del_irq,
 };
 
 static int __devinit hvc_vio_probe(struct vio_dev *vdev,
diff --git a/drivers/char/hvc_xen.c b/drivers/char/hvc_xen.c
index db2ae4216279..6b70aa66a587 100644
--- a/drivers/char/hvc_xen.c
+++ b/drivers/char/hvc_xen.c
@@ -100,6 +100,8 @@ static int read_console(uint32_t vtermno, char *buf, int len)
 static struct hv_ops hvc_ops = {
         .get_chars = read_console,
         .put_chars = write_console,
+        .notifier_add = notifier_add_irq,
+        .notifier_del = notifier_del_irq,
 };
 
 static int __init xen_init(void)