[S390] cio: introduce isc_(un)register functions.

This interface makes it easy for drivers to register usage of different
I/O interruption subclasses without needing to worry about possible
other users of the same isc.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

1 files changed, 68 insertions, 0 deletions

diff --git a/drivers/s390/cio/isc.c b/drivers/s390/cio/isc.c
new file mode 100644
index 000000000000..c592087be0f1
--- /dev/null
+++ b/drivers/s390/cio/isc.c
@@ -0,0 +1,68 @@
+/*
+ * Functions for registration of I/O interruption subclasses on s390.
+ *
+ * Copyright IBM Corp. 2008
+ * Authors: Sebastian Ott <sebott@linux.vnet.ibm.com>
+ */
+
+#include <linux/spinlock.h>
+#include <linux/module.h>
+#include <asm/isc.h>
+
+static unsigned int isc_refs[MAX_ISC + 1];
+static DEFINE_SPINLOCK(isc_ref_lock);
+
+
+/**
+ * isc_register - register an I/O interruption subclass.
+ * @isc: I/O interruption subclass to register
+ *
+ * The number of users for @isc is increased. If this is the first user to
+ * register @isc, the corresponding I/O interruption subclass mask is enabled.
+ *
+ * Context:
+ *   This function must not be called in interrupt context.
+ */
+void isc_register(unsigned int isc)
+{
+        if (isc > MAX_ISC) {
+                WARN_ON(1);
+                return;
+        }
+
+        spin_lock(&isc_ref_lock);
+        if (isc_refs[isc] == 0)
+                ctl_set_bit(6, 31 - isc);
+        isc_refs[isc]++;
+        spin_unlock(&isc_ref_lock);
+}
+EXPORT_SYMBOL_GPL(isc_register);
+
+/**
+ * isc_unregister - unregister an I/O interruption subclass.
+ * @isc: I/O interruption subclass to unregister
+ *
+ * The number of users for @isc is decreased. If this is the last user to
+ * unregister @isc, the corresponding I/O interruption subclass mask is
+ * disabled.
+ * Note: This function must not be called if isc_register() hasn't been called
+ * before by the driver for @isc.
+ *
+ * Context:
+ *   This function must not be called in interrupt context.
+ */
+void isc_unregister(unsigned int isc)
+{
+        spin_lock(&isc_ref_lock);
+        /* check for misuse */
+        if (isc > MAX_ISC || isc_refs[isc] == 0) {
+                WARN_ON(1);
+                goto out_unlock;
+        }
+        if (isc_refs[isc] == 1)
+                ctl_clear_bit(6, 31 - isc);
+        isc_refs[isc]--;
+out_unlock:
+        spin_unlock(&isc_ref_lock);
+}
+EXPORT_SYMBOL_GPL(isc_unregister);