i386/pc: factor out cxl range start to helper

Factor out the calculation of the base address of the memory region.
It will be used later on for the cxl range end counterpart calculation
and as well in pc_memory_init() CXL memory region initialization, thus
avoiding duplication.

Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20220719170014.27028-7-joao.m.martins@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/pc.c

@@ -825,6 +825,22 @@ static hwaddr pc_above_4g_end(PCMachineState *pcms)
     return x86ms->above_4g_mem_start + x86ms->above_4g_mem_size;
 }
 
+static uint64_t pc_get_cxl_range_start(PCMachineState *pcms)
+{
+    PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
+    MachineState *machine = MACHINE(pcms);
+    hwaddr cxl_base;
+
+    if (pcmc->has_reserved_memory && machine->device_memory->base) {
+        cxl_base = machine->device_memory->base
+            + memory_region_size(&machine->device_memory->mr);
+    } else {
+        cxl_base = pc_above_4g_end(pcms);
+    }
+
+    return cxl_base;
+}
+
 static uint64_t pc_get_cxl_range_end(PCMachineState *pcms)
 {
     uint64_t start = 0;
@@ -946,13 +962,7 @@ void pc_memory_init(PCMachineState *pcms,
         MemoryRegion *mr = &pcms->cxl_devices_state.host_mr;
         hwaddr cxl_size = MiB;
 
-        if (pcmc->has_reserved_memory && machine->device_memory->base) {
-            cxl_base = machine->device_memory->base
-                + memory_region_size(&machine->device_memory->mr);
-        } else {
-            cxl_base = pc_above_4g_end(pcms);
-        }
-
+        cxl_base = pc_get_cxl_range_start(pcms);
         e820_add_entry(cxl_base, cxl_size, E820_RESERVED);
         memory_region_init(mr, OBJECT(machine), "cxl_host_reg", cxl_size);
         memory_region_add_subregion(system_memory, cxl_base, mr);