drm/i915/guc: Allow preempt-client to be NULL

In the next patch, we may only conditionally allocate the preempt-client
if there is a global preempt context and so we need to be prepared in
case the preempt-client itself is NULL.

v2: Grep for more preempt_client.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180207210544.26351-1-chris@chris-wilson.co.uk
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 3849ded..9e44ade 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2338,7 +2338,6 @@ static int i915_guc_info(struct seq_file *m, void *data)
 		return -ENODEV;
 
 	GEM_BUG_ON(!guc->execbuf_client);
-	GEM_BUG_ON(!guc->preempt_client);
 
 	seq_printf(m, "Doorbell map:\n");
 	seq_printf(m, "\t%*pb\n", GUC_NUM_DOORBELLS, guc->doorbell_bitmap);
@@ -2346,8 +2345,11 @@ static int i915_guc_info(struct seq_file *m, void *data)
 
 	seq_printf(m, "\nGuC execbuf client @ %p:\n", guc->execbuf_client);
 	i915_guc_client_info(m, dev_priv, guc->execbuf_client);
-	seq_printf(m, "\nGuC preempt client @ %p:\n", guc->preempt_client);
-	i915_guc_client_info(m, dev_priv, guc->preempt_client);
+	if (guc->preempt_client) {
+		seq_printf(m, "\nGuC preempt client @ %p:\n",
+			   guc->preempt_client);
+		i915_guc_client_info(m, dev_priv, guc->preempt_client);
+	}
 
 	i915_guc_log_info(m, dev_priv);