drm/i915/guc: Add support for data reporting in GuC responses

GuC may return additional data in the response message.
Format and meaning of this data is action specific. We will
use this non-negative data as a new success return value.
Currently used actions don't return data that way yet.

v2: fix prohibited space after '~' (Michel)
    update commit message (Daniele)
v3: rebase

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180326194829.58836-3-michal.wajdeczko@intel.com

drivers/gpu/drm/i915/intel_guc.c

@@ -366,6 +366,9 @@ int intel_guc_send_mmio(struct intel_guc *guc, const u32 *action, u32 len)
 				 " ret=%d status=0x%08X response=0x%08X\n",
 				 action[0], ret, status,
 				 I915_READ(SOFT_SCRATCH(15)));
+	} else {
+		/* Use data from the GuC response as our return value */
+		ret = INTEL_GUC_MSG_TO_DATA(status);
 	}
 
 	intel_uncore_forcewake_put(dev_priv, guc->send_regs.fw_domains);

drivers/gpu/drm/i915/intel_guc_ct.c

@@ -400,7 +400,9 @@ static int ctch_send(struct intel_guc *guc,
 		return err;
 	if (!INTEL_GUC_MSG_IS_RESPONSE_SUCCESS(*status))
 		return -EIO;
-	return 0;
+
+	/* Use data from the GuC status as our return value */
+	return INTEL_GUC_MSG_TO_DATA(*status);
 }
 
 /*
@@ -410,18 +412,18 @@ static int intel_guc_send_ct(struct intel_guc *guc, const u32 *action, u32 len)
 {
 	struct intel_guc_ct_channel *ctch = &guc->ct.host_channel;
 	u32 status = ~0; /* undefined */
-	int err;
+	int ret;
 
 	mutex_lock(&guc->send_mutex);
 
-	err = ctch_send(guc, ctch, action, len, &status);
-	if (unlikely(err)) {
+	ret = ctch_send(guc, ctch, action, len, &status);
+	if (unlikely(ret < 0)) {
 		DRM_ERROR("CT: send action %#X failed; err=%d status=%#X\n",
-			  action[0], err, status);
+			  action[0], ret, status);
 	}
 
 	mutex_unlock(&guc->send_mutex);
-	return err;
+	return ret;
 }
 
 /**