[PATCH] s390: SCLP device driver cleanup

From: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>

sclp: core driver cleanup

Details:
- moved signal shutdown (quiesce) handling into a separate file
- cleanup of SCLP core driver:
  . introduced driver states instead of bits
  . introduced request retry count and retry limit
  . sclp_add_request now returns an error code if a request couldn't be started
  . introduced separate request structure for init_mask requests to simplify
    code
  . request timer is now manually checked in sclp_sync_wait because timer
    interrupts are disabled in this context
  . removed busy timer - request timer now handles both cases
  . split up sclp_start_request into __sclp_start_request and sclp_process
    queue
  . removed sclp_error_message (unused)
  . introduced sclp_check_handler function to split up initial init mask
    test from standard init mask request processing
  . introduced sclp_deactivate and sclp_reactivate for simplified reboot
    event handling (and potential use in suspend/resume scenario)
  . added protection against multiple concurrent init mask calls
- minor changes in SCLP core driver:
  . updated comments
  . renamed functions to be consistent with "function name starts with __ =>
    needs lock"
  . renamed internal functions for consistency reasons
  . introduced inlined helper functions to simplify code
  . moved EXPORT_SYMBOL definitions next to function definition
- changes in sclp console driver
  . removed callback recursion to prevent stack overflow
- changes to CPI module
  . added check for sclp_add_request return code
  . changed printks to specify a message level
- changes to generic sclp tty layer
  . removed timed buffer retry after error (timers may not work in some
    situations)
  . introduced return code for sclp_emit_buffer
- changes to sclp tty driver
  . removed callback recursion
- changes to sclp vt220 driver
  . removed callback recursion
  . removed timed buffer retry after error
- modified sclp_init_mask to prevent problems with some compiler versions
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/s390/char/Makefile

@@ -11,7 +11,7 @@ obj-$(CONFIG_TN3270_FS) += fs3270.o
 
 obj-$(CONFIG_TN3215) += con3215.o
 
-obj-$(CONFIG_SCLP) += sclp.o sclp_rw.o
+obj-$(CONFIG_SCLP) += sclp.o sclp_rw.o sclp_quiesce.o
 obj-$(CONFIG_SCLP_TTY) += sclp_tty.o
 obj-$(CONFIG_SCLP_CONSOLE) += sclp_con.o
 obj-$(CONFIG_SCLP_VT220_TTY) += sclp_vt220.o

drivers/s390/char/sclp.h

@@ -95,6 +95,7 @@ struct sclp_req {
 	sclp_cmdw_t command;		/* sclp command to execute */
 	void	*sccb;			/* pointer to the sccb to execute */
 	char	status;			/* status of this request */
+	int     start_count;		/* number of SVCs done for this req */
 	/* Callback that is called after reaching final status. */
 	void (*callback)(struct sclp_req *, void *data);
 	void *callback_data;
@@ -123,12 +124,13 @@ struct sclp_register {
 };
 
 /* externals from sclp.c */
-void sclp_add_request(struct sclp_req *req);
+int sclp_add_request(struct sclp_req *req);
 void sclp_sync_wait(void);
 int sclp_register(struct sclp_register *reg);
 void sclp_unregister(struct sclp_register *reg);
-char *sclp_error_message(u16 response_code);
 int sclp_remove_processed(struct sccb_header *sccb);
+int sclp_deactivate(void);
+int sclp_reactivate(void);
 
 /* useful inlines */
 

drivers/s390/char/sclp_con.c

@@ -49,25 +49,22 @@ static void
 sclp_conbuf_callback(struct sclp_buffer *buffer, int rc)
 {
 	unsigned long flags;
-	struct sclp_buffer *next;
 	void *page;
 
-	/* Ignore return code - because console-writes aren't critical,
-	   we do without a sophisticated error recovery mechanism.  */
-	page = sclp_unmake_buffer(buffer);
-	spin_lock_irqsave(&sclp_con_lock, flags);
-	/* Remove buffer from outqueue */
-	list_del(&buffer->list);
-	sclp_con_buffer_count--;
-	list_add_tail((struct list_head *) page, &sclp_con_pages);
-	/* Check if there is a pending buffer on the out queue. */
-	next = NULL;
-	if (!list_empty(&sclp_con_outqueue))
-		next = list_entry(sclp_con_outqueue.next,
-				  struct sclp_buffer, list);
-	spin_unlock_irqrestore(&sclp_con_lock, flags);
-	if (next != NULL)
-		sclp_emit_buffer(next, sclp_conbuf_callback);
+	do {
+		page = sclp_unmake_buffer(buffer);
+		spin_lock_irqsave(&sclp_con_lock, flags);
+		/* Remove buffer from outqueue */
+		list_del(&buffer->list);
+		sclp_con_buffer_count--;
+		list_add_tail((struct list_head *) page, &sclp_con_pages);
+		/* Check if there is a pending buffer on the out queue. */
+		buffer = NULL;
+		if (!list_empty(&sclp_con_outqueue))
+			buffer = list_entry(sclp_con_outqueue.next,
+					    struct sclp_buffer, list);
+		spin_unlock_irqrestore(&sclp_con_lock, flags);
+	} while (buffer && sclp_emit_buffer(buffer, sclp_conbuf_callback));
 }
 
 static inline void
@@ -76,6 +73,7 @@ sclp_conbuf_emit(void)
 	struct sclp_buffer* buffer;
 	unsigned long flags;
 	int count;
+	int rc;
 
 	spin_lock_irqsave(&sclp_con_lock, flags);
 	buffer = sclp_conbuf;
@@ -87,8 +85,11 @@ sclp_conbuf_emit(void)
 	list_add_tail(&buffer->list, &sclp_con_outqueue);
 	count = sclp_con_buffer_count++;
 	spin_unlock_irqrestore(&sclp_con_lock, flags);
-	if (count == 0)
-		sclp_emit_buffer(buffer, sclp_conbuf_callback);
+	if (count)
+		return;
+	rc = sclp_emit_buffer(buffer, sclp_conbuf_callback);
+	if (rc)
+		sclp_conbuf_callback(buffer, rc);
 }
 
 /*

drivers/s390/char/sclp_cpi.c

@@ -196,18 +196,20 @@ cpi_module_init(void)
 	rc = sclp_register(&sclp_cpi_event);
 	if (rc) {
 		/* could not register sclp event. Die. */
-		printk("cpi: could not register to hardware console.\n");
+		printk(KERN_WARNING "cpi: could not register to hardware "
+		       "console.\n");
 		return -EINVAL;
 	}
 	if (!(sclp_cpi_event.sclp_send_mask & EvTyp_CtlProgIdent_Mask)) {
-		printk("cpi: no control program identification support\n");
+		printk(KERN_WARNING "cpi: no control program identification "
+		       "support\n");
 		sclp_unregister(&sclp_cpi_event);
 		return -ENOTSUPP;
 	}
 
 	req = cpi_prepare_req();
 	if (IS_ERR(req)) {
-		printk("cpi: couldn't allocate request\n");
+		printk(KERN_WARNING "cpi: couldn't allocate request\n");
 		sclp_unregister(&sclp_cpi_event);
 		return PTR_ERR(req);
 	}
@@ -216,13 +218,20 @@ cpi_module_init(void)
 	sema_init(&sem, 0);
 	req->callback_data = &sem;
 	/* Add request to sclp queue */
-	sclp_add_request(req);
+	rc = sclp_add_request(req);
+	if (rc) {
+		printk(KERN_WARNING "cpi: could not start request\n");
+		cpi_free_req(req);
+		sclp_unregister(&sclp_cpi_event);
+		return rc;
+	}
 	/* make "insmod" sleep until callback arrives */
 	down(&sem);
 
 	rc = ((struct cpi_sccb *) req->sccb)->header.response_code;
 	if (rc != 0x0020) {
-		printk("cpi: failed with response code 0x%x\n", rc);
+		printk(KERN_WARNING "cpi: failed with response code 0x%x\n",
+		       rc);
 		rc = -ECOMM;
 	} else
 		rc = 0;

drivers/s390/char/sclp_quiesce.c

+/*
+ *  drivers/s390/char/sclp_quiesce.c
+ *     signal quiesce handler
+ *
+ *  (C) Copyright IBM Corp. 1999,2004
+ *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
+ *             Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/cpumask.h>
+#include <linux/smp.h>
+#include <linux/init.h>
+#include <asm/atomic.h>
+#include <asm/ptrace.h>
+#include <asm/sigp.h>
+
+#include "sclp.h"
+
+
+#ifdef CONFIG_SMP
+/* Signal completion of shutdown process. All CPUs except the first to enter
+ * this function: go to stopped state. First CPU: wait until all other
+ * CPUs are in stopped or check stop state. Afterwards, load special PSW
+ * to indicate completion. */
+static void
+do_load_quiesce_psw(void * __unused)
+{
+	static atomic_t cpuid = ATOMIC_INIT(-1);
+	psw_t quiesce_psw;
+	__u32 status;
+	int i;
+
+	if (atomic_compare_and_swap(-1, smp_processor_id(), &cpuid))
+		signal_processor(smp_processor_id(), sigp_stop);
+	/* Wait for all other cpus to enter stopped state */
+	i = 1;
+	while (i < NR_CPUS) {
+		if (!cpu_online(i)) {
+			i++;
+			continue;
+		}
+		switch (signal_processor_ps(&status, 0, i, sigp_sense)) {
+		case sigp_order_code_accepted:
+		case sigp_status_stored:
+			/* Check for stopped and check stop state */
+			if (status & 0x50)
+				i++;
+			break;
+		case sigp_busy:
+			break;
+		case sigp_not_operational:
+			i++;
+			break;
+		}
+	}
+	/* Quiesce the last cpu with the special psw */
+	quiesce_psw.mask = PSW_BASE_BITS | PSW_MASK_WAIT;
+	quiesce_psw.addr = 0xfff;
+	__load_psw(quiesce_psw);
+}
+
+/* Shutdown handler. Perform shutdown function on all CPUs. */
+static void
+do_machine_quiesce(void)
+{
+	on_each_cpu(do_load_quiesce_psw, NULL, 0, 0);
+}
+#else
+/* Shutdown handler. Signal completion of shutdown by loading special PSW. */
+static void
+do_machine_quiesce(void)
+{
+	psw_t quiesce_psw;
+
+	quiesce_psw.mask = PSW_BASE_BITS | PSW_MASK_WAIT;
+	quiesce_psw.addr = 0xfff;
+	__load_psw(quiesce_psw);
+}
+#endif
+
+extern void ctrl_alt_del(void);
+
+/* Handler for quiesce event. Start shutdown procedure. */
+static void
+sclp_quiesce_handler(struct evbuf_header *evbuf)
+{
+	_machine_restart = (void *) do_machine_quiesce;
+	_machine_halt = do_machine_quiesce;
+	_machine_power_off = do_machine_quiesce;
+	ctrl_alt_del();
+}
+
+static struct sclp_register sclp_quiesce_event = {
+	.receive_mask = EvTyp_SigQuiesce_Mask,
+	.receiver_fn = sclp_quiesce_handler
+};
+
+/* Initialize quiesce driver. */
+static int __init
+sclp_quiesce_init(void)
+{
+	int rc;
+
+	rc = sclp_register(&sclp_quiesce_event);
+	if (rc)
+		printk(KERN_WARNING "sclp: could not register quiesce handler "
+		       "(rc=%d)\n", rc);
+	return rc;
+}
+
+module_init(sclp_quiesce_init);

drivers/s390/char/sclp_rw.c

@@ -54,7 +54,6 @@ sclp_make_buffer(void *page, unsigned short columns, unsigned short htab)
 	buffer = ((struct sclp_buffer *) ((addr_t) sccb + PAGE_SIZE)) - 1;
 	buffer->sccb = sccb;
 	buffer->retry_count = 0;
-	init_timer(&buffer->retry_timer);
 	buffer->mto_number = 0;
 	buffer->mto_char_sum = 0;
 	buffer->current_line = NULL;
@@ -365,17 +364,7 @@ sclp_rw_init(void)
 	return rc;
 }
 
-static void
-sclp_buffer_retry(unsigned long data)
-{
-	struct sclp_buffer *buffer = (struct sclp_buffer *) data;
-	buffer->request.status = SCLP_REQ_FILLED;
-	buffer->sccb->header.response_code = 0x0000;
-	sclp_add_request(&buffer->request);
-}
-
-#define SCLP_BUFFER_MAX_RETRY		5
-#define	SCLP_BUFFER_RETRY_INTERVAL	2
+#define SCLP_BUFFER_MAX_RETRY		1
 
 /*
  * second half of Write Event Data-function that has to be done after
@@ -404,7 +393,7 @@ sclp_writedata_callback(struct sclp_req *request, void *data)
 		break;
 
 	case 0x0340: /* Contained SCLP equipment check */
-		if (buffer->retry_count++ > SCLP_BUFFER_MAX_RETRY) {
+		if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
 			rc = -EIO;
 			break;
 		}
@@ -413,26 +402,26 @@ sclp_writedata_callback(struct sclp_req *request, void *data)
 			/* not all buffers were processed */
 			sccb->header.response_code = 0x0000;
 			buffer->request.status = SCLP_REQ_FILLED;
-			sclp_add_request(request);
-			return;
-		}
-		rc = 0;
+			rc = sclp_add_request(request);
+			if (rc == 0)
+				return;
+		} else
+			rc = 0;
 		break;
 
 	case 0x0040: /* SCLP equipment check */
 	case 0x05f0: /* Target resource in improper state */
-		if (buffer->retry_count++ > SCLP_BUFFER_MAX_RETRY) {
+		if (++buffer->retry_count > SCLP_BUFFER_MAX_RETRY) {
 			rc = -EIO;
 			break;
 		}
-		/* wait some time, then retry request */
-		buffer->retry_timer.function = sclp_buffer_retry;
-		buffer->retry_timer.data = (unsigned long) buffer;
-		buffer->retry_timer.expires = jiffies +
-						SCLP_BUFFER_RETRY_INTERVAL*HZ;
-		add_timer(&buffer->retry_timer);
-		return;
-
+		/* retry request */
+		sccb->header.response_code = 0x0000;
+		buffer->request.status = SCLP_REQ_FILLED;
+		rc = sclp_add_request(request);
+		if (rc == 0)
+			return;
+		break;
 	default:
 		if (sccb->header.response_code == 0x71f0)
 			rc = -ENOMEM;
@@ -446,9 +435,10 @@ sclp_writedata_callback(struct sclp_req *request, void *data)
 
 /*
  * Setup the request structure in the struct sclp_buffer to do SCLP Write
- * Event Data and pass the request to the core SCLP loop.
+ * Event Data and pass the request to the core SCLP loop. Return zero on
+ * success, non-zero otherwise.
  */
-void
+int
 sclp_emit_buffer(struct sclp_buffer *buffer,
 		 void (*callback)(struct sclp_buffer *, int))
 {
@@ -459,11 +449,8 @@ sclp_emit_buffer(struct sclp_buffer *buffer,
 		sclp_finalize_mto(buffer);
 
 	/* Are there messages in the output buffer ? */
-	if (buffer->mto_number == 0) {
-		if (callback != NULL)
-			callback(buffer, 0);
-		return;
-	}
+	if (buffer->mto_number == 0)
+		return -EIO;
 
 	sccb = buffer->sccb;
 	if (sclp_rw_event.sclp_send_mask & EvTyp_Msg_Mask)
@@ -472,16 +459,13 @@ sclp_emit_buffer(struct sclp_buffer *buffer,
 	else if (sclp_rw_event.sclp_send_mask & EvTyp_PMsgCmd_Mask)
 		/* Use write priority message */
 		sccb->msg_buf.header.type = EvTyp_PMsgCmd;
-	else {
-		if (callback != NULL)
-			callback(buffer, -ENOSYS);
-		return;
-	}
+	else
+		return -ENOSYS;
 	buffer->request.command = SCLP_CMDW_WRITEDATA;
 	buffer->request.status = SCLP_REQ_FILLED;
 	buffer->request.callback = sclp_writedata_callback;
 	buffer->request.callback_data = buffer;
 	buffer->request.sccb = sccb;
 	buffer->callback = callback;
-	sclp_add_request(&buffer->request);
+	return sclp_add_request(&buffer->request);
 }

drivers/s390/char/sclp_rw.h

@@ -12,7 +12,6 @@
 #define __SCLP_RW_H__
 
 #include <linux/list.h>
-#include <linux/timer.h>
 
 struct mto {
 	u16 length;
@@ -74,7 +73,6 @@ struct sclp_buffer {
 	char *current_line;
 	int current_length;
 	int retry_count;
-	struct timer_list retry_timer;
 	/* output format settings */
 	unsigned short columns;
 	unsigned short htab;
@@ -90,7 +88,7 @@ struct sclp_buffer *sclp_make_buffer(void *, unsigned short, unsigned short);
 void *sclp_unmake_buffer(struct sclp_buffer *);
 int sclp_buffer_space(struct sclp_buffer *);
 int sclp_write(struct sclp_buffer *buffer, const unsigned char *, int);
-void sclp_emit_buffer(struct sclp_buffer *,void (*)(struct sclp_buffer *,int));
+int sclp_emit_buffer(struct sclp_buffer *,void (*)(struct sclp_buffer *,int));
 void sclp_set_columns(struct sclp_buffer *, unsigned short);
 void sclp_set_htab(struct sclp_buffer *, unsigned short);
 int sclp_chars_in_buffer(struct sclp_buffer *);

drivers/s390/char/sclp_tty.c

@@ -255,25 +255,22 @@ static void
 sclp_ttybuf_callback(struct sclp_buffer *buffer, int rc)
 {
 	unsigned long flags;
-	struct sclp_buffer *next;
 	void *page;
 
-	/* Ignore return code - because tty-writes aren't critical,
-	   we do without a sophisticated error recovery mechanism.  */
-	page = sclp_unmake_buffer(buffer);
-	spin_lock_irqsave(&sclp_tty_lock, flags);
-	/* Remove buffer from outqueue */
-	list_del(&buffer->list);
-	sclp_tty_buffer_count--;
-	list_add_tail((struct list_head *) page, &sclp_tty_pages);
-	/* Check if there is a pending buffer on the out queue. */
-	next = NULL;
-	if (!list_empty(&sclp_tty_outqueue))
-		next = list_entry(sclp_tty_outqueue.next,
-				  struct sclp_buffer, list);
-	spin_unlock_irqrestore(&sclp_tty_lock, flags);
-	if (next != NULL)
-		sclp_emit_buffer(next, sclp_ttybuf_callback);
+	do {
+		page = sclp_unmake_buffer(buffer);
+		spin_lock_irqsave(&sclp_tty_lock, flags);
+		/* Remove buffer from outqueue */
+		list_del(&buffer->list);
+		sclp_tty_buffer_count--;
+		list_add_tail((struct list_head *) page, &sclp_tty_pages);
+		/* Check if there is a pending buffer on the out queue. */
+		buffer = NULL;
+		if (!list_empty(&sclp_tty_outqueue))
+			buffer = list_entry(sclp_tty_outqueue.next,
+					    struct sclp_buffer, list);
+		spin_unlock_irqrestore(&sclp_tty_lock, flags);
+	} while (buffer && sclp_emit_buffer(buffer, sclp_ttybuf_callback));
 	wake_up(&sclp_tty_waitq);
 	/* check if the tty needs a wake up call */
 	if (sclp_tty != NULL) {
@@ -286,14 +283,17 @@ __sclp_ttybuf_emit(struct sclp_buffer *buffer)
 {
 	unsigned long flags;
 	int count;
+	int rc;
 
 	spin_lock_irqsave(&sclp_tty_lock, flags);
 	list_add_tail(&buffer->list, &sclp_tty_outqueue);
 	count = sclp_tty_buffer_count++;
 	spin_unlock_irqrestore(&sclp_tty_lock, flags);
-
-	if (count == 0)
-		sclp_emit_buffer(buffer, sclp_ttybuf_callback);
+	if (count)
+		return;
+	rc = sclp_emit_buffer(buffer, sclp_ttybuf_callback);
+	if (rc)
+		sclp_ttybuf_callback(buffer, rc);
 }
 
 /*

drivers/s390/char/sclp_vt220.c

@@ -42,7 +42,6 @@ struct sclp_vt220_request {
 	struct list_head list;
 	struct sclp_req sclp_req;
 	int retry_count;
-	struct timer_list retry_timer;
 };
 
 /* VT220 SCCB */
@@ -96,7 +95,7 @@ static int sclp_vt220_initialized = 0;
 static int sclp_vt220_flush_later;
 
 static void sclp_vt220_receiver_fn(struct evbuf_header *evbuf);
-static void __sclp_vt220_emit(struct sclp_vt220_request *request);
+static int __sclp_vt220_emit(struct sclp_vt220_request *request);
 static void sclp_vt220_emit_current(void);
 
 /* Registration structure for our interest in SCLP event buffers */
@@ -116,25 +115,24 @@ static void
 sclp_vt220_process_queue(struct sclp_vt220_request *request)
 {
 	unsigned long flags;
-	struct sclp_vt220_request *next;
 	void *page;
 
-	/* Put buffer back to list of empty buffers */
-	page = request->sclp_req.sccb;
-	spin_lock_irqsave(&sclp_vt220_lock, flags);
-	/* Move request from outqueue to empty queue */
-	list_del(&request->list);
-	sclp_vt220_outqueue_count--;
-	list_add_tail((struct list_head *) page, &sclp_vt220_empty);
-	/* Check if there is a pending buffer on the out queue. */
-	next = NULL;
-	if (!list_empty(&sclp_vt220_outqueue))
-		next = list_entry(sclp_vt220_outqueue.next,
-				  struct sclp_vt220_request, list);
-	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
-	if (next != NULL)
-		__sclp_vt220_emit(next);
-	else if (sclp_vt220_flush_later)
+	do {
+		/* Put buffer back to list of empty buffers */
+		page = request->sclp_req.sccb;
+		spin_lock_irqsave(&sclp_vt220_lock, flags);
+		/* Move request from outqueue to empty queue */
+		list_del(&request->list);
+		sclp_vt220_outqueue_count--;
+		list_add_tail((struct list_head *) page, &sclp_vt220_empty);
+		/* Check if there is a pending buffer on the out queue. */
+		request = NULL;
+		if (!list_empty(&sclp_vt220_outqueue))
+			request = list_entry(sclp_vt220_outqueue.next,
+					     struct sclp_vt220_request, list);
+		spin_unlock_irqrestore(&sclp_vt220_lock, flags);
+	} while (request && __sclp_vt220_emit(request));
+	if (request == NULL && sclp_vt220_flush_later)
 		sclp_vt220_emit_current();
 	wake_up(&sclp_vt220_waitq);
 	/* Check if the tty needs a wake up call */
@@ -143,25 +141,7 @@ sclp_vt220_process_queue(struct sclp_vt220_request *request)
 	}
 }
 
-/*
- * Retry sclp write request after waiting some time for an sclp equipment
- * check to pass.
- */
-static void
-sclp_vt220_retry(unsigned long data)
-{
-	struct sclp_vt220_request *request;
-	struct sclp_vt220_sccb *sccb;
-
-	request = (struct sclp_vt220_request *) data;
-	request->sclp_req.status = SCLP_REQ_FILLED;
-	sccb = (struct sclp_vt220_sccb *) request->sclp_req.sccb;
-	sccb->header.response_code = 0x0000;
-	sclp_add_request(&request->sclp_req);
-}
-
-#define SCLP_BUFFER_MAX_RETRY		5
-#define	SCLP_BUFFER_RETRY_INTERVAL	2
+#define SCLP_BUFFER_MAX_RETRY		1
 
 /*
  * Callback through which the result of a write request is reported by the
@@ -189,29 +169,26 @@ sclp_vt220_callback(struct sclp_req *request, void *data)
 		break;
 
 	case 0x0340: /* Contained SCLP equipment check */
-		if (vt220_request->retry_count++ > SCLP_BUFFER_MAX_RETRY)
+		if (++vt220_request->retry_count > SCLP_BUFFER_MAX_RETRY)
 			break;
 		/* Remove processed buffers and requeue rest */
 		if (sclp_remove_processed((struct sccb_header *) sccb) > 0) {
 			/* Not all buffers were processed */
 			sccb->header.response_code = 0x0000;
 			vt220_request->sclp_req.status = SCLP_REQ_FILLED;
-			sclp_add_request(request);
-			return;
+			if (sclp_add_request(request) == 0)
+				return;
 		}
 		break;
 
 	case 0x0040: /* SCLP equipment check */
-		if (vt220_request->retry_count++ > SCLP_BUFFER_MAX_RETRY)
+		if (++vt220_request->retry_count > SCLP_BUFFER_MAX_RETRY)
 			break;
-		/* Wait some time, then retry request */
-		vt220_request->retry_timer.function = sclp_vt220_retry;
-		vt220_request->retry_timer.data =
-			(unsigned long) vt220_request;
-		vt220_request->retry_timer.expires =
-			jiffies + SCLP_BUFFER_RETRY_INTERVAL*HZ;
-		add_timer(&vt220_request->retry_timer);
-		return;
+		sccb->header.response_code = 0x0000;
+		vt220_request->sclp_req.status = SCLP_REQ_FILLED;
+		if (sclp_add_request(request) == 0)
+			return;
+		break;
 
 	default:
 		break;
@@ -220,22 +197,22 @@ sclp_vt220_callback(struct sclp_req *request, void *data)
 }
 
 /*
- * Emit vt220 request buffer to SCLP.
+ * Emit vt220 request buffer to SCLP. Return zero on success, non-zero
+ * otherwise.
  */
-static void
+static int
 __sclp_vt220_emit(struct sclp_vt220_request *request)
 {
 	if (!(sclp_vt220_register.sclp_send_mask & EvTyp_VT220Msg_Mask)) {
 		request->sclp_req.status = SCLP_REQ_FAILED;
-		sclp_vt220_callback(&request->sclp_req, (void *) request);
-		return;
+		return -EIO;
 	}
 	request->sclp_req.command = SCLP_CMDW_WRITEDATA;
 	request->sclp_req.status = SCLP_REQ_FILLED;
 	request->sclp_req.callback = sclp_vt220_callback;
 	request->sclp_req.callback_data = (void *) request;
 
-	sclp_add_request(&request->sclp_req);
+	return sclp_add_request(&request->sclp_req);
 }
 
 /*
@@ -253,12 +230,12 @@ sclp_vt220_emit(struct sclp_vt220_request *request)
 	spin_unlock_irqrestore(&sclp_vt220_lock, flags);
 	/* Emit only the first buffer immediately - callback takes care of
 	 * the rest */
-	if (count == 0)
-		__sclp_vt220_emit(request);
+	if (count == 0 && __sclp_vt220_emit(request))
+		sclp_vt220_process_queue(request);
 }
 
 /*
- * Queue and emit current request.
+ * Queue and emit current request. Return zero on success, non-zero otherwise.
  */
 static void
 sclp_vt220_emit_current(void)
@@ -300,7 +277,6 @@ sclp_vt220_initialize_page(void *page)
 	/* Place request structure at end of page */
 	request = ((struct sclp_vt220_request *)
 			((addr_t) page + PAGE_SIZE)) - 1;
-	init_timer(&request->retry_timer);
 	request->retry_count = 0;
 	request->sclp_req.sccb = page;
 	/* SCCB goes at start of page */