s390/zcrypt: make sysfs reset attribute trigger queue reset

Until now there is no way to reset a AP queue or card. Driving a card
or queue offline and online again does only toggle the 'software'
online state. The only way to trigger a (hardware) reset is by running
hot-unplug/hot-plug for example on the HMC.

This patch makes the queue reset attribute in sysfs writable.
Writing into this attribute triggers a reset on the AP queue's state
machine. So the AP queue is flushed and state machine runs through the
initial states which cause a reset (PQAP(RAPQ)) and a re-registration
to interrupts (PQAP(AQIC)) if available.

The reset sysfs attribute is writable by root only. So only an
administrator is allowed to initiate a reset of AP queues. Please note
that the queue's counter values are left untouched by the reset.
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/crypto/ap_queue.c

@@ -14,6 +14,9 @@
 #include <asm/facility.h>
 
 #include "ap_bus.h"
+#include "ap_debug.h"
+
+static void __ap_flush_queue(struct ap_queue *aq);
 
 /**
  * ap_queue_enable_interruption(): Enable interruption on an AP queue.
@@ -541,7 +544,25 @@ static ssize_t reset_show(struct device *dev,
 	return rc;
 }
 
-static DEVICE_ATTR_RO(reset);
+static ssize_t reset_store(struct device *dev,
+			   struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	struct ap_queue *aq = to_ap_queue(dev);
+
+	spin_lock_bh(&aq->lock);
+	__ap_flush_queue(aq);
+	aq->state = AP_STATE_RESET_START;
+	ap_wait(ap_sm_event(aq, AP_EVENT_POLL));
+	spin_unlock_bh(&aq->lock);
+
+	AP_DBF(DBF_INFO, "reset queue=%02x.%04x triggered by user\n",
+	       AP_QID_CARD(aq->qid), AP_QID_QUEUE(aq->qid));
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(reset);
 
 static ssize_t interrupt_show(struct device *dev,
 			      struct device_attribute *attr, char *buf)