drm/i915/uc: Extract common code from GuC stop/disable comm

During normal driver unload we attempt to disable GuC communication
while it is currently stopped. This results in a nop'd call to
intel_guc_ct_disable within guc_disable_communication because
stop/disable rely on the same flag to prevent further comms with CT.

We can avoid the call to disable and still leave communication in a
satisfactory state by extracting a set of shared steps from stop/disable.
This set can include guc_disable_interrupts as we do not require the
single caller of guc_stop_communication to be atomic:
"drm/i915/selftests: Fixup atomic reset checking".

This situation (stop -> disable) only occurs during intel_uc_fini_hw,
so during fini, call guc_disable_communication only if currently enabled.
The symmetric calls to enable/disable remain unmodified for all other
scenarios.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110943
Signed-off-by: Fernando Pacheco <[e-mail]>
Cc: Chris Wilson <[e-mail]>
Cc: Michal Wajdeczko <[e-mail]>
Cc: Daniele Ceraolo Spurio <[e-mail]>
Reviewed-by: Daniele Ceraolo Spurio <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

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

···
 	return 0;
 }
 
-static void guc_stop_communication(struct intel_guc *guc)
-{
-	intel_guc_ct_stop(&guc->ct);
-
-	guc->send = intel_guc_send_nop;
-	guc->handler = intel_guc_to_host_event_handler_nop;
-
-	guc_clear_mmio_msg(guc);
-}
-
-static void guc_disable_communication(struct intel_guc *guc)
+static void __guc_stop_communication(struct intel_guc *guc)
 {
 	/*
 	 * Events generated during or after CT disable are logged by guc in
···
 
 	guc->send = intel_guc_send_nop;
 	guc->handler = intel_guc_to_host_event_handler_nop;
+}
+
+static void guc_stop_communication(struct intel_guc *guc)
+{
+	intel_guc_ct_stop(&guc->ct);
+
+	__guc_stop_communication(guc);
+
+	DRM_INFO("GuC communication stopped\n");
+}
+
+static void guc_disable_communication(struct intel_guc *guc)
+{
+	__guc_stop_communication(guc);
 
 	intel_guc_ct_disable(&guc->ct);
 
···
 	if (intel_uc_supports_guc_submission(uc))
 		intel_guc_submission_disable(guc);
 
-	guc_disable_communication(guc);
+	if (guc_communication_enabled(guc))
+		guc_disable_communication(guc);
+
 	__uc_sanitize(uc);
 }