Create per-CPU mutex for XSCOM usage.

Change-Id: I76ad5c1d553d544b52910afd82e2716781ea13b9
Reviewed-on: http://gfw160.austin.ibm.com:8080/gerrit/140
Tested-by: Jenkins Server
Reviewed-by: Thi N. Tran <thi@us.ibm.com>
Reviewed-by: Douglas R. Gilbert <dgilbert@us.ibm.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/src/lib/syscall_mmio.C b/src/lib/syscall_mmio.C
index 30ec5bd37..83498798b 100644
--- a/src/lib/syscall_mmio.C
+++ b/src/lib/syscall_mmio.C
@@ -1,5 +1,8 @@
 #include <sys/syscall.h>
 #include <sys/mmio.h>
+#include <assert.h>
+#include <kernel/task.H>
+#include <kernel/cpu.H>
 
 using namespace Systemcalls;
 
@@ -22,3 +25,35 @@ int mmio_hmer_write(uint64_t value)
 {
     return (int)(int64_t)_syscall1(MMIO_HMER_WRITE, (void*)value);
 }
+
+mutex_t mmio_xscom_mutex()
+{
+    // Get task structure.
+    register task_t* task;
+    asm volatile("mr %0, 13" : "=r"(task));
+
+    // Ensure task is pinned.
+    assert(task->affinity_pinned);
+
+    // Get mutex from cpu structure.
+    mutex_t mutex = task->cpu->xscom_mutex;
+
+    // Create mutex if not created.
+    if (NULL == mutex)
+    {
+        mutex = mutex_create();
+
+        // Atomically update xscom_mutex with new mutex.
+        if (!__sync_bool_compare_and_swap(&task->cpu->xscom_mutex, NULL, mutex))
+        {
+            // Failed, some other thread beat us to it.
+
+            // Destroy mutex and get one created by other thread in the
+            // meantime.
+            mutex_destroy(mutex);
+            mutex = task->cpu->xscom_mutex;
+        }
+    }
+
+    return mutex;
+}