libcamera: software_isp: debayer: Introduce a start() / stop() methods to the debayer object

In order to initialise and deinitialise gpuisp we need to be able to setup
EGL in the same thread as Debayer::process() happens in.

This requires extending the Debayer object to provide start and stop
methods which are triggered through invokeMethod in the same way as
process() is.

Introduce start() and stop() methods to the Debayer class. Trigger those
methods as described above via invokeMethod. The debayer_egl class will
take care of initialising and de-initialising as necessary. Debayer CPU
sees no functional change.

Per feedback from Barnabas the stop method is using blocking
synchronisation and thus we drop ispWorkerThread_.removeMessages().

[bod: Made method blocking not queued per Robert's bugfixes]
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/software_isp/software_isp.cpp

@@ -347,7 +347,9 @@ int SoftwareIsp::start()
 		return ret;
 
 	ispWorkerThread_.start();
-	return 0;
+
+	return debayer_->invokeMethod(&DebayerCpu::start,
+				      ConnectionTypeBlocking);
 }
 
 /**
@@ -358,9 +360,11 @@ int SoftwareIsp::start()
  */
 void SoftwareIsp::stop()
 {
+	debayer_->invokeMethod(&DebayerCpu::stop,
+			       ConnectionTypeBlocking);
+
 	ispWorkerThread_.exit();
 	ispWorkerThread_.wait();
-	ispWorkerThread_.removeMessages(debayer_.get());
 
 	Thread::current()->dispatchMessages(Message::Type::InvokeMessage, this);