target/riscv: Add some event callbacks.

Specifically, call into the RISC-V version when target becomes halted,
running, or unavailable.

I'll be using unavailable shortly.

Change-Id: I9ffffdccbf22e053fe6390d656b362bf9ab9559a
Signed-off-by: Tim Newsome <tim@sifive.com>

src/target/riscv/riscv.c

@@ -2752,6 +2752,10 @@ static int riscv_poll_hart(struct target *target, enum riscv_next_action *next_a
 					}
 				}
 
+				if (r->handle_became_halted &&
+						r->handle_became_halted(target, previous_riscv_state) != ERROR_OK)
+					return ERROR_FAIL;
+
 				/* We shouldn't do the callbacks yet. What if
 				 * there are multiple harts that halted at the
 				 * same time? We need to set debug reason on each
@@ -2769,12 +2773,18 @@ static int riscv_poll_hart(struct target *target, enum riscv_next_action *next_a
 				LOG_TARGET_DEBUG(target, "  triggered running");
 				target->state = TARGET_RUNNING;
 				target->debug_reason = DBG_REASON_NOTHALTED;
+				if (r->handle_became_running &&
+						r->handle_became_running(target, previous_riscv_state) != ERROR_OK)
+					return ERROR_FAIL;
 				break;
 
 			case RISCV_STATE_UNAVAILABLE:
 				LOG_TARGET_DEBUG(target, "  became unavailable");
 				LOG_TARGET_INFO(target, "became unavailable.");
 				target->state = TARGET_UNAVAILABLE;
+				if (r->handle_became_unavailable &&
+						r->handle_became_unavailable(target, previous_riscv_state) != ERROR_OK)
+					return ERROR_FAIL;
 				break;
 
 			case RISCV_STATE_NON_EXISTENT:

src/target/riscv/riscv.h

@@ -193,6 +193,17 @@ struct riscv_info {
 	 * was resumed. */
 	int (*resume_go)(struct target *target);
 	int (*step_current_hart)(struct target *target);
+
+	/* These get called from riscv_poll_hart(), which is a house of cards
+	 * together with openocd_poll(), so be careful not to upset things too
+	 * much. */
+	int (*handle_became_halted)(struct target *target,
+		enum riscv_hart_state previous_riscv_state);
+	int (*handle_became_running)(struct target *target,
+		enum riscv_hart_state previous_riscv_state);
+	int (*handle_became_unavailable)(struct target *target,
+		enum riscv_hart_state previous_riscv_state);
+
 	/* Get this target as ready as possible to resume, without actually
 	 * resuming. */
 	int (*resume_prep)(struct target *target);