s390/sclp: add parameter to specify number of buffer pages

Add a kernel parameter to be able to specify the number of pages to be
used as output buffer by the line-mode sclp driver and the vt220 sclp
driver. The current number of output pages is 6, if the service element
is unavailable the boot messages alone can fill up the output buffer.
If this happens the system blocks until the service element is working
again. For a large LPAR with many devices it is sensible to have the
ability to increase the output buffer size. To help to debug this
situation add a counter for the page-pool-empty situation and make it
available as a sclp driver attribute.
To avoid the system to stall until the service element works again
add another kernel parameter to allow to drop output buffers.

Signed-off-by: Martin Schwidefsky <[e-mail]>

drivers/s390/char/sclp.c

···
 /* Suspend request */
 static DECLARE_COMPLETION(sclp_request_queue_flushed);
 
+/* Number of console pages to allocate, used by sclp_con.c and sclp_vt220.c */
+int sclp_console_pages = SCLP_CONSOLE_PAGES;
+/* Flag to indicate if buffer pages are dropped on buffer full condition */
+int sclp_console_drop = 0;
+/* Number of times the console dropped buffer pages */
+unsigned long sclp_console_full;
+
 static void sclp_suspend_req_cb(struct sclp_req *req, void *data)
 {
 	complete(&sclp_request_queue_flushed);
 }
+
+static int __init sclp_setup_console_pages(char *str)
+{
+	int pages, rc;
+
+	rc = kstrtoint(str, 0, &pages);
+	if (!rc && pages >= SCLP_CONSOLE_PAGES)
+		sclp_console_pages = pages;
+	return 1;
+}
+
+__setup("sclp_con_pages=", sclp_setup_console_pages);
+
+static int __init sclp_setup_console_drop(char *str)
+{
+	int drop, rc;
+
+	rc = kstrtoint(str, 0, &drop);
+	if (!rc && drop)
+		sclp_console_drop = 1;
+	return 1;
+}
+
+__setup("sclp_con_drop=", sclp_setup_console_drop);
 
 static struct sclp_req sclp_suspend_req;
 
···
 	.restore	= sclp_restore,
 };
 
+static ssize_t sclp_show_console_pages(struct device_driver *dev, char *buf)
+{
+	return sprintf(buf, "%i\n", sclp_console_pages);
+}
+
+static DRIVER_ATTR(con_pages, S_IRUSR, sclp_show_console_pages, NULL);
+
+static ssize_t sclp_show_con_drop(struct device_driver *dev, char *buf)
+{
+	return sprintf(buf, "%i\n", sclp_console_drop);
+}
+
+static DRIVER_ATTR(con_drop, S_IRUSR, sclp_show_con_drop, NULL);
+
+static ssize_t sclp_show_console_full(struct device_driver *dev, char *buf)
+{
+	return sprintf(buf, "%lu\n", sclp_console_full);
+}
+
+static DRIVER_ATTR(con_full, S_IRUSR, sclp_show_console_full, NULL);
+
+static struct attribute *sclp_drv_attrs[] = {
+	&driver_attr_con_pages.attr,
+	&driver_attr_con_drop.attr,
+	&driver_attr_con_full.attr,
+	NULL,
+};
+static struct attribute_group sclp_drv_attr_group = {
+	.attrs = sclp_drv_attrs,
+};
+static const struct attribute_group *sclp_drv_attr_groups[] = {
+	&sclp_drv_attr_group,
+	NULL,
+};
+
 static struct platform_driver sclp_pdrv = {
 	.driver = {
 		.name	= "sclp",
 		.owner	= THIS_MODULE,
 		.pm	= &sclp_pm_ops,
+		.groups = sclp_drv_attr_groups,
 	},
 };
 
···
 	rc = platform_driver_register(&sclp_pdrv);
 	if (rc)
 		return rc;
+
 	sclp_pdev = platform_device_register_simple("sclp", -1, NULL, 0);
 	rc = IS_ERR(sclp_pdev) ? PTR_ERR(sclp_pdev) : 0;
 	if (rc)
 		goto fail_platform_driver_unregister;
+
 	rc = atomic_notifier_chain_register(&panic_notifier_list,
 					    &sclp_on_panic_nb);
 	if (rc)

drivers/s390/char/sclp.h

···
 
 /* maximum number of pages concerning our own memory management */
 #define MAX_KMEM_PAGES (sizeof(unsigned long) << 3)
-#define MAX_CONSOLE_PAGES	6
+#define SCLP_CONSOLE_PAGES	6
 
 #define EVTYP_OPCMD		0x01
 #define EVTYP_MSG		0x02
···
 
 int sclp_sdias_init(void);
 void sclp_sdias_exit(void);
+
+extern int sclp_console_pages;
+extern int sclp_console_drop;
+extern unsigned long sclp_console_full;
 
 /* useful inlines */
 

drivers/s390/char/sclp_con.c

···
 }
 
 /*
+ * Drop oldest console buffer if sclp_con_drop is set
+ */
+static int
+sclp_console_drop_buffer(void)
+{
+	struct list_head *list;
+	struct sclp_buffer *buffer;
+	void *page;
+
+	if (!sclp_console_drop)
+		return 0;
+	list = sclp_con_outqueue.next;
+	if (sclp_con_queue_running)
+		/* The first element is in I/O */
+		list = list->next;
+	if (list == &sclp_con_outqueue)
+		return 0;
+	list_del(list);
+	buffer = list_entry(list, struct sclp_buffer, list);
+	page = sclp_unmake_buffer(buffer);
+	list_add_tail((struct list_head *) page, &sclp_con_pages);
+	return 1;
+}
+
+/*
  * Writes the given message to S390 system console
  */
 static void
···
 	do {
 		/* make sure we have a console output buffer */
 		if (sclp_conbuf == NULL) {
+			if (list_empty(&sclp_con_pages))
+				sclp_console_full++;
 			while (list_empty(&sclp_con_pages)) {
 				if (sclp_con_suspended)
 					goto out;
+				if (sclp_console_drop_buffer())
+					break;
 				spin_unlock_irqrestore(&sclp_con_lock, flags);
 				sclp_sync_wait();
 				spin_lock_irqsave(&sclp_con_lock, flags);
···
 		return rc;
 	/* Allocate pages for output buffering */
 	INIT_LIST_HEAD(&sclp_con_pages);
-	for (i = 0; i < MAX_CONSOLE_PAGES; i++) {
+	for (i = 0; i < sclp_console_pages; i++) {
 		page = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
 		list_add_tail(page, &sclp_con_pages);
 	}

drivers/s390/char/sclp_vt220.c

···
 
 #define BUFFER_MAX_DELAY	HZ/20
 
+/*
+ * Drop oldest console buffer if sclp_con_drop is set
+ */
+static int
+sclp_vt220_drop_buffer(void)
+{
+	struct list_head *list;
+	struct sclp_vt220_request *request;
+	void *page;
+
+	if (!sclp_console_drop)
+		return 0;
+	list = sclp_vt220_outqueue.next;
+	if (sclp_vt220_queue_running)
+		/* The first element is in I/O */
+		list = list->next;
+	if (list == &sclp_vt220_outqueue)
+		return 0;
+	list_del(list);
+	request = list_entry(list, struct sclp_vt220_request, list);
+	page = request->sclp_req.sccb;
+	list_add_tail((struct list_head *) page, &sclp_vt220_empty);
+	return 1;
+}
+
 /* 
  * Internal implementation of the write function. Write COUNT bytes of data
  * from memory at BUF
···
 	do {
 		/* Create an sclp output buffer if none exists yet */
 		if (sclp_vt220_current_request == NULL) {
+			if (list_empty(&sclp_vt220_empty))
+				sclp_console_full++;
 			while (list_empty(&sclp_vt220_empty)) {
-				spin_unlock_irqrestore(&sclp_vt220_lock, flags);
 				if (may_fail || sclp_vt220_suspended)
 					goto out;
-				else
-					sclp_sync_wait();
+				if (sclp_vt220_drop_buffer())
+					break;
+				spin_unlock_irqrestore(&sclp_vt220_lock, flags);
+
+				sclp_sync_wait();
 				spin_lock_irqsave(&sclp_vt220_lock, flags);
 			}
 			page = (void *) sclp_vt220_empty.next;
···
 		sclp_vt220_timer.expires = jiffies + BUFFER_MAX_DELAY;
 		add_timer(&sclp_vt220_timer);
 	}
-	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
 out:
+	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
 	return overall_written;
 }
 
···
 
 	if (!CONSOLE_IS_SCLP)
 		return 0;
-	rc = __sclp_vt220_init(MAX_CONSOLE_PAGES);
+	rc = __sclp_vt220_init(sclp_console_pages);
 	if (rc)
 		return rc;
 	/* Attach linux console */