drm/i915/guc: Verify result from CTB (de)register action

In commit b839a869 ("drm/i915/guc: Add support for data
reporting in GuC responses") we missed the hypothetical case
that GuC might return positive non-zero value as success data.

While that would be lucky treated as error case, and at the
end will result in reporting valid -EIO, in the meantime this
value will be passed to ERR_PTR that could be misleading.

v2: rebased
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210926184545.1407-2-michal.wajdeczko@intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c

@@ -168,12 +168,15 @@ static int guc_action_register_ct_buffer(struct intel_guc *guc, u32 type,
 		FIELD_PREP(HOST2GUC_REGISTER_CTB_REQUEST_MSG_2_DESC_ADDR, desc_addr),
 		FIELD_PREP(HOST2GUC_REGISTER_CTB_REQUEST_MSG_3_BUFF_ADDR, buff_addr),
 	};
+	int ret;
 
 	GEM_BUG_ON(type != GUC_CTB_TYPE_HOST2GUC && type != GUC_CTB_TYPE_GUC2HOST);
 	GEM_BUG_ON(size % SZ_4K);
 
 	/* CT registration must go over MMIO */
-	return intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
+	ret = intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
+
+	return ret > 0 ? -EPROTO : ret;
 }
 
 static int ct_register_buffer(struct intel_guc_ct *ct, u32 type,
@@ -201,11 +204,14 @@ static int guc_action_deregister_ct_buffer(struct intel_guc *guc, u32 type)
 		FIELD_PREP(GUC_HXG_REQUEST_MSG_0_ACTION, GUC_ACTION_HOST2GUC_DEREGISTER_CTB),
 		FIELD_PREP(HOST2GUC_DEREGISTER_CTB_REQUEST_MSG_1_TYPE, type),
 	};
+	int ret;
 
 	GEM_BUG_ON(type != GUC_CTB_TYPE_HOST2GUC && type != GUC_CTB_TYPE_GUC2HOST);
 
 	/* CT deregistration must go over MMIO */
-	return intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
+	ret = intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
+
+	return ret > 0 ? -EPROTO : ret;
 }
 
 static int ct_deregister_buffer(struct intel_guc_ct *ct, u32 type)