genesys: Simplify lamp warmup setup on gl843

backend/genesys/device.h

@@ -100,6 +100,16 @@ struct MethodResolutions
         return *std::min_element(resolutions_x.begin(), resolutions_x.end());
     }
 
+    unsigned get_nearest_resolution_x(unsigned resolution) const
+    {
+        return *std::min_element(resolutions_x.begin(), resolutions_x.end(),
+                                 [&](unsigned lhs, unsigned rhs)
+        {
+            return std::abs(static_cast<int>(lhs) - static_cast<int>(resolution)) <
+                     std::abs(static_cast<int>(rhs) - static_cast<int>(resolution));
+        });
+    }
+
     unsigned get_min_resolution_y() const
     {
         return *std::min_element(resolutions_y.begin(), resolutions_y.end());

backend/genesys/gl843.cpp

@@ -1752,14 +1752,11 @@ void CommandSetGl843::init_regs_for_warmup(Genesys_Device* dev, const Genesys_Se
                                            int* total_size) const
 {
     DBG_HELPER(dbg);
-  int dpihw;
-  int resolution;
+    (void) sensor;
 
-  /* setup scan */
-  *channels=3;
-  resolution=600;
-    dpihw = sensor.get_register_hwdpi(resolution);
-  resolution=dpihw;
+    *channels=3;
+    unsigned resolution = dev->model->get_resolution_settings(dev->settings.scan_method)
+                                     .get_nearest_resolution_x(600);
 
   const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution, *channels,
                                                        dev->settings.scan_method);