drm/i915/guc: Implement response handling in send_mmio()

We're using data encoded in the status MMIO as return value from send
function, but GuC may also write more data in remaining MMIO regs.
Let's copy content of these registers to the buffer provided by caller.

v2: new line (Michel)
v3: updated commit message
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Oscar Mateo <oscar.mateo@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/20180326194829.58836-5-michal.wajdeczko@intel.com

drivers/gpu/drm/i915/intel_guc.c

@@ -368,11 +368,20 @@ 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 {
+		goto out;
+	}
+
+	if (response_buf) {
+		int count = min(response_buf_size, guc->send_regs.count - 1);
+
+		for (i = 0; i < count; i++)
+			response_buf[i] = I915_READ(guc_send_reg(guc, i + 1));
+	}
+
 	/* Use data from the GuC response as our return value */
 	ret = INTEL_GUC_MSG_TO_DATA(status);
-	}
 
+out:
 	intel_uncore_forcewake_put(dev_priv, guc->send_regs.fw_domains);
 	mutex_unlock(&guc->send_mutex);