[Intel-gfx] [RFC] drm/i915/guc: Enable guc logging on guc log relay write

[Robert M. Fosha]

Creating and opening the GuC log relay file enables and starts
the relay potentially before the caller is ready to consume logs.
Change the behavior so that relay starts only on an explicit call
to the write function (with a value of '1'). Other values flush
the log relay as before.

Cc: Matthew Brost <matthew.brost at intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
Signed-off-by: Robert M. Fosha <robert.m.fosha at intel.com>
---
 drivers/gpu/drm/i915/gt/uc/intel_guc_log.c | 38 +++++++++++++++++-----
 drivers/gpu/drm/i915/gt/uc/intel_guc_log.h |  2 ++
 drivers/gpu/drm/i915/i915_debugfs.c        | 27 +++++++++++++--
 3 files changed, 56 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
index 36332064de9c..9a98270d05b6 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.c
@@ -361,6 +361,7 @@ void intel_guc_log_init_early(struct intel_guc_log *log)
 {
 	mutex_init(&log->relay.lock);
 	INIT_WORK(&log->relay.flush_work, capture_logs_work);
+	log->relay_started = false;
 }
 
 static int guc_log_relay_create(struct intel_guc_log *log)
@@ -585,15 +586,6 @@ int intel_guc_log_relay_open(struct intel_guc_log *log)
 
 	mutex_unlock(&log->relay.lock);
 
-	guc_log_enable_flush_events(log);
-
-	/*
-	 * When GuC is logging without us relaying to userspace, we're ignoring
-	 * the flush notification. This means that we need to unconditionally
-	 * flush on relay enabling, since GuC only notifies us once.
-	 */
-	queue_work(system_highpri_wq, &log->relay.flush_work);
-
 	return 0;
 
 out_relay:
@@ -604,12 +596,38 @@ int intel_guc_log_relay_open(struct intel_guc_log *log)
 	return ret;
 }
 
+int intel_guc_log_relay_start(struct intel_guc_log *log)
+{
+	int ret = 0;
+
+	if (log->relay_started) {
+		ret =  -EEXIST;
+	} else {
+		guc_log_enable_flush_events(log);
+
+		/*
+		 * When GuC is logging without us relaying to userspace, we're
+		 * ignoring the flush notification. This means that we need to
+		 * unconditionally * flush on relay enabling, since GuC only
+		 * notifies us once.
+		 */
+		queue_work(system_highpri_wq, &log->relay.flush_work);
+
+		log->relay_started = false;
+	}
+
+	return ret;
+}
+
 void intel_guc_log_relay_flush(struct intel_guc_log *log)
 {
 	struct intel_guc *guc = log_to_guc(log);
 	struct drm_i915_private *i915 = guc_to_gt(guc)->i915;
 	intel_wakeref_t wakeref;
 
+	if (!log->relay_started)
+		return;
+
 	/*
 	 * Before initiating the forceful flush, wait for any pending/ongoing
 	 * flush to complete otherwise forceful flush may not actually happen.
@@ -638,6 +656,8 @@ void intel_guc_log_relay_close(struct intel_guc_log *log)
 	guc_log_unmap(log);
 	guc_log_relay_destroy(log);
 	mutex_unlock(&log->relay.lock);
+
+	log->relay_started = false;
 }
 
 void intel_guc_log_handle_flush_event(struct intel_guc_log *log)
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.h
index 6f764879acb1..ecf7a49416b4 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_log.h
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_log.h
@@ -44,6 +44,7 @@ struct intel_guc;
 
 struct intel_guc_log {
 	u32 level;
+	bool relay_started;
 	struct i915_vma *vma;
 	struct {
 		void *buf_addr;
@@ -67,6 +68,7 @@ void intel_guc_log_destroy(struct intel_guc_log *log);
 int intel_guc_log_set_level(struct intel_guc_log *log, u32 level);
 bool intel_guc_log_relay_enabled(const struct intel_guc_log *log);
 int intel_guc_log_relay_open(struct intel_guc_log *log);
+int intel_guc_log_relay_start(struct intel_guc_log *log);
 void intel_guc_log_relay_flush(struct intel_guc_log *log);
 void intel_guc_log_relay_close(struct intel_guc_log *log);
 
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 708855e051b5..c3683fdd0deb 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2049,9 +2049,32 @@ i915_guc_log_relay_write(struct file *filp,
 			 loff_t *ppos)
 {
 	struct intel_guc_log *log = filp->private_data;
+	char *input_buffer;
+	int val;
+	int ret;
 
-	intel_guc_log_relay_flush(log);
-	return cnt;
+	input_buffer = memdup_user_nul(ubuf, cnt);
+	if (IS_ERR(input_buffer))
+		return PTR_ERR(input_buffer);
+
+	ret = kstrtoint(input_buffer, 10, &val);
+	if (ret < 0)
+		goto out;
+
+	/*
+	 * Enable and start the guc log relay on value of 1.
+	 * Flush log relay for any other value.
+	 */
+	if (val == 1) {
+		ret = intel_guc_log_relay_start(log);
+	} else {
+		intel_guc_log_relay_flush(log);
+		ret = cnt;
+	}
+
+out:
+	kfree(input_buffer);
+	return ret;
 }
 
 static int i915_guc_log_relay_release(struct inode *inode, struct file *file)
-- 
2.21.0.5.gaeb582a983