Report only compatible GPU, i.e. no GPU if mixed/double precision is requested by the hardware does not support it

lib/gpu/lal_device.cpp

@@ -1039,10 +1039,18 @@ Device<PRECISION,ACC_PRECISION> global_device;
 
 using namespace LAMMPS_AL;
 
-bool lmp_has_gpu_device()
+// check if a suitable GPU is present.
+// for mixed and double precision GPU library compilation
+// also the GPU needs to support double precision.
+bool lmp_has_compatible_gpu_device()
 {
   UCL_Device gpu;
-  return (gpu.num_platforms() > 0);
+  bool compatible_gpu = gpu.num_platforms() > 0;
+  #if defined(_SINGLE_DOUBLE) || defined(_DOUBLE_DOUBLE)
+  if (!gpu.double_precision(0))
+    compatible_gpu = false;
+  #endif
+  return compatible_gpu;
 }
 
 std::string lmp_gpu_device_info()

src/info.cpp

@@ -1146,12 +1146,14 @@ bool Info::has_package(const std::string &package_name) {
 
 #if defined(LMP_GPU)
 extern bool lmp_gpu_config(const std::string &, const std::string &);
-extern bool lmp_has_gpu_device();
+extern bool lmp_has_compatible_gpu_device();
 extern std::string lmp_gpu_device_info();
 
+// we will only report compatible GPUs, i.e. when a GPU device is
+// available *and* supports the required floating point precision
 bool Info::has_gpu_device()
 {
-  return lmp_has_gpu_device();
+  return lmp_has_compatible_gpu_device();
 }
 
 std::string Info::get_gpu_device_info()

src/lammps.cpp

@@ -1340,7 +1340,7 @@ void LAMMPS::print_config(FILE *fp)
   fmt::print(fp,"Accelerator configuration:\n\n{}\n",
              Info::get_accelerator_info());
 #if defined(LMP_GPU)
-  fmt::print(fp,"GPU present: {}\n\n",Info::has_gpu_device() ? "yes" : "no");
+  fmt::print(fp,"Compatible GPU present: {}\n\n",Info::has_gpu_device() ? "yes" : "no");
 #endif
 
   fputs("Active compile time flags:\n\n",fp);