cpu: Don't change to suspend if the thread status is halted (#1039)

In our gem5 model, there are four types represent thread context:
Active, Suspend, Halting and Halted


5641c5e464/src/cpu/thread_context.hh (L99-L117)

When initializing the gem5 instance, all of the thread contexts are set
Halted. The status of thread context will not be active until the
Workload initializes start up, except the StubWorkload. So if the user
uses the StubWorkload, and the CPU is connected with the model_reset
port. The thread context of the CPU will be activated possibly.

The following is the steps of activating thread context of the CPU
without Workload[1] initialization or lower model_reset port[2].

1. Raise the model_reset port (Change the state from Halted to Suspend)
5641c5e464/src/cpu/base.cc (L671-L673)

2. Post the interrupt to CPU (Change the state from Suspend to Active)
5641c5e464/src/cpu/base.cc (L231-L239)

Implementation of wakeup

SimpleCPU:

5641c5e464/src/cpu/simple/base.cc (L251-L259)

MinorCPU:

5641c5e464/src/cpu/minor/cpu.cc (L143-L151)

O3CPU:

5641c5e464/src/cpu/o3/cpu.cc (L1337-L1346)

This CL fixed the issue when raising the model reset port to CPU(let CPU
sleep) if the CPU is not activated by workload. If the CPU status is
halted, it's should not change to Suspend to avoid wake up

Reference

The model_reset is introduced in the CL:
https://gem5-review.googlesource.com/c/public/gem5/+/67574/4

[1] Activate by workload (ARM example):

5641c5e464/src/arch/arm/fs_workload.cc (L101-L114)

[2] Lower the model_reset:

5641c5e464/src/cpu/base.cc (L191-L192)
5641c5e464/src/cpu/base.cc (L674-L685)

Change-Id: I5bfc0b7491d14369fff77b98b71c0ac763fb7c42

src/cpu/o3/thread_context.cc

@@ -86,7 +86,9 @@ ThreadContext::suspend()
     DPRINTF(O3CPU, "Calling suspend on Thread Context %d\n",
             threadId());
 
-    if (thread->status() == gem5::ThreadContext::Suspended)
+    if (thread->status() == gem5::ThreadContext::Suspended ||
+        thread->status() == gem5::ThreadContext::Halting ||
+        thread->status() == gem5::ThreadContext::Halted)
         return;
 
     if (cpu->isDraining()) {

src/cpu/simple_thread.cc

@@ -143,7 +143,8 @@ SimpleThread::activate()
 void
 SimpleThread::suspend()
 {
-    if (status() == ThreadContext::Suspended)
+    if (status() == ThreadContext::Suspended ||
+        status() == ThreadContext::Halted)
         return;
 
     lastActivate = curTick();