[S390] ETR support.

This patch adds support for clock synchronization to an external time
reference (ETR). The external time reference sends an oscillator
signal and a synchronization signal every 2^20 microseconds to keep
the TOD clocks of all connected servers in sync. For availability
two ETR units can be connected to a machine. If the clock deviates
for more than the sync-check tolerance all cpus get a machine check
that indicates that the clock is out of sync. For the lovely details
how to get the clock back in sync see the code below.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 39 insertions, 18 deletions

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index f208940c463c..555e18a6b781 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -1232,6 +1232,19 @@ __dasd_process_blk_queue(struct dasd_device * device)
                 if (IS_ERR(cqr)) {
                         if (PTR_ERR(cqr) == -ENOMEM)
                                 break;  /* terminate request queue loop */
+                        if (PTR_ERR(cqr) == -EAGAIN) {
+                                /*
+                                 * The current request cannot be build right
+                                 * now, we have to try later. If this request
+                                 * is the head-of-queue we stop the device
+                                 * for 1/2 second.
+                                 */
+                                if (!list_empty(&device->ccw_queue))
+                                        break;
+                                device->stopped |= DASD_STOPPED_PENDING;
+                                dasd_set_timer(device, HZ/2);
+                                break;
+                        }
                         DBF_DEV_EVENT(DBF_ERR, device,
                                       "CCW creation failed (rc=%ld) "
                                       "on request %p",
diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index d59115cce6dc..a17d73193aab 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -204,37 +204,39 @@ recs_per_track(struct dasd_eckd_characteristics * rdc,
         return 0;
 }
 
-static inline void
+static inline int
 check_XRC (struct ccw1         *de_ccw,
            struct DE_eckd_data *data,
            struct dasd_device  *device)
 {
         struct dasd_eckd_private *private;
+        int rc;
 
         private = (struct dasd_eckd_private *) device->private;
+        if (!private->rdc_data.facilities.XRC_supported)
+                return 0;
 
         /* switch on System Time Stamp - needed for XRC Support */
-        if (private->rdc_data.facilities.XRC_supported) {
-
-                data->ga_extended |= 0x08; /* switch on 'Time Stamp Valid'   */
-                data->ga_extended |= 0x02; /* switch on 'Extended Parameter' */
-
-                data->ep_sys_time = get_clock ();
-
-                de_ccw->count = sizeof (struct DE_eckd_data);
-                de_ccw->flags |= CCW_FLAG_SLI;
-        }
+        data->ga_extended |= 0x08; /* switch on 'Time Stamp Valid'   */
+        data->ga_extended |= 0x02; /* switch on 'Extended Parameter' */
 
-        return;
+        rc = get_sync_clock(&data->ep_sys_time);
+        /* Ignore return code if sync clock is switched off. */
+        if (rc == -ENOSYS || rc == -EACCES)
+                rc = 0;
 
-} /* end check_XRC */
+        de_ccw->count = sizeof (struct DE_eckd_data);
+        de_ccw->flags |= CCW_FLAG_SLI;
+        return rc;
+}
 
-static inline void
+static inline int
 define_extent(struct ccw1 * ccw, struct DE_eckd_data * data, int trk,
               int totrk, int cmd, struct dasd_device * device)
 {
         struct dasd_eckd_private *private;
         struct ch_t geo, beg, end;
+        int rc = 0;
 
         private = (struct dasd_eckd_private *) device->private;
 
@@ -263,12 +265,12 @@ define_extent(struct ccw1 * ccw, struct DE_eckd_data * data, int trk,
         case DASD_ECKD_CCW_WRITE_KD_MT:
                 data->mask.perm = 0x02;
                 data->attributes.operation = private->attrib.operation;
-                check_XRC (ccw, data, device);
+                rc = check_XRC (ccw, data, device);
                 break;
         case DASD_ECKD_CCW_WRITE_CKD:
         case DASD_ECKD_CCW_WRITE_CKD_MT:
                 data->attributes.operation = DASD_BYPASS_CACHE;
-                check_XRC (ccw, data, device);
+                rc = check_XRC (ccw, data, device);
                 break;
         case DASD_ECKD_CCW_ERASE:
         case DASD_ECKD_CCW_WRITE_HOME_ADDRESS:
@@ -276,7 +278,7 @@ define_extent(struct ccw1 * ccw, struct DE_eckd_data * data, int trk,
                 data->mask.perm = 0x3;
                 data->mask.auth = 0x1;
                 data->attributes.operation = DASD_BYPASS_CACHE;
-                check_XRC (ccw, data, device);
+                rc = check_XRC (ccw, data, device);
                 break;
         default:
                 DEV_MESSAGE(KERN_ERR, device, "unknown opcode 0x%x", cmd);
@@ -312,6 +314,7 @@ define_extent(struct ccw1 * ccw, struct DE_eckd_data * data, int trk,
         data->beg_ext.head = beg.head;
         data->end_ext.cyl = end.cyl;
         data->end_ext.head = end.head;
+        return rc;
 }
 
 static inline void
@@ -1200,7 +1203,12 @@ dasd_eckd_build_cp(struct dasd_device * device, struct request *req)
                 return cqr;
         ccw = cqr->cpaddr;
         /* First ccw is define extent. */
-        define_extent(ccw++, cqr->data, first_trk, last_trk, cmd, device);
+        if (define_extent(ccw++, cqr->data, first_trk,
+                          last_trk, cmd, device) == -EAGAIN) {
+                /* Clock not in sync and XRC is enabled. Try again later. */
+                dasd_sfree_request(cqr, device);
+                return ERR_PTR(-EAGAIN);
+        }
         /* Build locate_record+read/write/ccws. */
         idaws = (unsigned long *) (cqr->data + sizeof(struct DE_eckd_data));
         LO_data = (struct LO_eckd_data *) (idaws + cidaw);