accel/tcg: Make TCGCPUOps::cpu_exec_halt mandatory

Now that all targets set TCGCPUOps::cpu_exec_halt, we can make it
mandatory and remove the fallback handling that calls cpu_has_work.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

accel/tcg/cpu-exec.c

@@ -682,13 +682,8 @@ static inline bool cpu_handle_halt(CPUState *cpu)
 #ifndef CONFIG_USER_ONLY
     if (cpu->halted) {
         const TCGCPUOps *tcg_ops = cpu->cc->tcg_ops;
-        bool leave_halt;
+        bool leave_halt = tcg_ops->cpu_exec_halt(cpu);
 
-        if (tcg_ops->cpu_exec_halt) {
-            leave_halt = tcg_ops->cpu_exec_halt(cpu);
-        } else {
-            leave_halt = cpu_has_work(cpu);
-        }
         if (!leave_halt) {
             return true;
         }
@@ -1082,6 +1077,10 @@ bool tcg_exec_realizefn(CPUState *cpu, Error **errp)
     static bool tcg_target_initialized;
 
     if (!tcg_target_initialized) {
+        /* Check mandatory TCGCPUOps handlers */
+#ifndef CONFIG_USER_ONLY
+        assert(cpu->cc->tcg_ops->cpu_exec_halt);
+#endif /* !CONFIG_USER_ONLY */
         cpu->cc->tcg_ops->initialize();
         tcg_target_initialized = true;
     }

include/hw/core/tcg-cpu-ops.h

@@ -122,10 +122,13 @@ struct TCGCPUOps {
      * to do when the CPU is in the halted state.
      *
      * Return true to indicate that the CPU should now leave halt, false
-     * if it should remain in the halted state.
+     * if it should remain in the halted state. (This should generally
+     * be the same value that cpu_has_work() would return.)
      *
-     * If this method is not provided, the default is to do nothing, and
-     * to leave halt if cpu_has_work() returns true.
+     * This method must be provided. If the target does not need to
+     * do anything special for halt, the same function used for its
+     * CPUClass::has_work method can be used here, as they have the
+     * same function signature.
      */
     bool (*cpu_exec_halt)(CPUState *cpu);
     /**