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>

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

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

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))];

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>

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;
+}

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,

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,

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)