gpu: nvgpu: empty FECS buffer on trace enable

Currently, when reading from ctxsw device node, we are collecting
traces that occurred before enabling tracing. This is not wanted,
and makes testing unpredicatable.
This change drops existing data in FECS ring buffer when enabling
traces, as currently done on vm-server side.

Jira EVLR-991

Change-Id: Idd2544d4667396f90778b7be82bdf73d1f8b8dc8
Signed-off-by: Thomas Fleury <tfleury@nvidia.com>
Reviewed-on: http://git-master/r/1293303
Reviewed-by: Vishnu Reddy Mandalapu <vmandalapu@nvidia.com>
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

1 files changed, 19 insertions, 7 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/fecs_trace_gk20a.c b/drivers/gpu/nvgpu/gk20a/fecs_trace_gk20a.c
index 6b77dff5..1f86fd8f 100644
--- a/drivers/gpu/nvgpu/gk20a/fecs_trace_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/fecs_trace_gk20a.c
@@ -720,15 +720,27 @@ static int gk20a_fecs_trace_enable(struct gk20a *g)
 {
         struct gk20a_fecs_trace *trace = g->fecs_trace;
         struct task_struct *task;
+        int write;
 
-        if (!trace->poll_task) {
-                task = kthread_run(gk20a_fecs_trace_periodic_polling, g, __func__);
-                if (unlikely(IS_ERR(task))) {
-                        gk20a_warn(dev_from_gk20a(g), "failed to create FECS polling task");
-                        return PTR_ERR(task);
-                }
-                trace->poll_task = task;
+        if (!trace)
+                return -EINVAL;
+
+        if  (trace->poll_task)
+                return 0;
+
+        /* drop data in hw buffer */
+        if (g->ops.fecs_trace.flush)
+                g->ops.fecs_trace.flush(g);
+        write = gk20a_fecs_trace_get_write_index(g);
+        gk20a_fecs_trace_set_read_index(g, write);
+
+        task = kthread_run(gk20a_fecs_trace_periodic_polling, g, __func__);
+        if (unlikely(IS_ERR(task))) {
+                gk20a_warn(dev_from_gk20a(g),
+                                "failed to create FECS polling task");
+                return PTR_ERR(task);
         }
+        trace->poll_task = task;
 
         return 0;
 }