drm/i915/guc: Enable send function only after successful init

It is safer to setup valid send function after successful GuC
hardware initialization. In addition we prepare placeholder
where we can setup any alternate GuC communication mechanism.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170502103243.54940-1-michal.wajdeczko@intel.com
[ickle: Fixup ENODEV for an impossible error path]
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_uc.c

@@ -99,7 +99,7 @@ void intel_uc_init_early(struct drm_i915_private *dev_priv)
 	struct intel_guc *guc = &dev_priv->guc;
 
 	mutex_init(&guc->send_mutex);
-	guc->send = intel_guc_send_mmio;
+	guc->send = intel_guc_send_nop;
 }
 
 static void fetch_uc_fw(struct drm_i915_private *dev_priv,
@@ -252,13 +252,27 @@ void intel_uc_fini_fw(struct drm_i915_private *dev_priv)
 	__intel_uc_fw_fini(&dev_priv->huc.fw);
 }
 
+static int guc_enable_communication(struct intel_guc *guc)
+{
+	/* XXX: placeholder for alternate setup */
+	guc->send = intel_guc_send_mmio;
+	return 0;
+}
+
+static void guc_disable_communication(struct intel_guc *guc)
+{
+	guc->send = intel_guc_send_nop;
+}
+
 int intel_uc_init_hw(struct drm_i915_private *dev_priv)
 {
+	struct intel_guc *guc = &dev_priv->guc;
 	int ret, attempts;
 
 	if (!i915.enable_guc_loading)
 		return 0;
 
+	guc_disable_communication(guc);
 	gen9_reset_guc_interrupts(dev_priv);
 
 	/* We need to notify the guc whenever we change the GGTT */
@@ -308,6 +322,10 @@ int intel_uc_init_hw(struct drm_i915_private *dev_priv)
 	if (ret)
 		goto err_submission;
 
+	ret = guc_enable_communication(guc);
+	if (ret)
+		goto err_submission;
+
 	intel_guc_auth_huc(dev_priv);
 	if (i915.enable_guc_submission) {
 		if (i915.guc_log_level >= 0)
@@ -330,6 +348,7 @@ int intel_uc_init_hw(struct drm_i915_private *dev_priv)
 	 * marks the GPU as wedged until reset).
 	 */
 err_interrupts:
+	guc_disable_communication(guc);
 	gen9_disable_guc_interrupts(dev_priv);
 err_submission:
 	if (i915.enable_guc_submission)
@@ -364,6 +383,12 @@ void intel_uc_fini_hw(struct drm_i915_private *dev_priv)
 	i915_ggtt_disable_guc(dev_priv);
 }
 
+int intel_guc_send_nop(struct intel_guc *guc, const u32 *action, u32 len)
+{
+	WARN(1, "Unexpected send: action=%#x\n", *action);
+	return -ENODEV;
+}
+
 /*
  * This function implements the MMIO based host to GuC interface.
  */

drivers/gpu/drm/i915/intel_uc.h

@@ -227,6 +227,7 @@ void intel_uc_fini_fw(struct drm_i915_private *dev_priv);
 int intel_uc_init_hw(struct drm_i915_private *dev_priv);
 void intel_uc_fini_hw(struct drm_i915_private *dev_priv);
 int intel_guc_sample_forcewake(struct intel_guc *guc);
+int intel_guc_send_nop(struct intel_guc *guc, const u32 *action, u32 len);
 int intel_guc_send_mmio(struct intel_guc *guc, const u32 *action, u32 len);
 static inline int intel_guc_send(struct intel_guc *guc, const u32 *action, u32 len)
 {