Make poll backoff time based.

Requested in https://review.openocd.org/c/openocd/+/6964.
I'm making the change here so I have a chance to test it properly before
pushing it upstream.

A nice effect of this change is that we avoid some unnecessary polling
early on when gdb is connecting and we would poll once every time we
send gdb a qXfer packet.

Change-Id: I4bdb9f05839e8c1e01ff6dde49d6589595418095
Signed-off-by: Tim Newsome <tim@sifive.com>

2 files changed, 34 insertions, 34 deletions

diff --git a/src/target/target.c b/src/target/target.c
index 7d3861a..3a56513 100644
--- a/src/target/target.c
+++ b/src/target/target.c
@@ -3046,44 +3046,41 @@ static int handle_target(void *priv)
 			is_jtag_poll_safe() && target;
 			target = target->next) {
 
-		if (!target->tap->enabled)
+		/* This function only gets called every polling_interval, so
+		 * allow some slack in the time comparison. Otherwise, if we
+		 * schedule for now+polling_interval, the next poll won't
+		 * actually happen until a polling_interval later. */
+		if (!target->tap->enabled ||
+		    power_dropout ||
+		    srst_asserted ||
+		    timeval_ms() + polling_interval / 2 < target->backoff.next_attempt)
 			continue;
 
-		if (target->backoff.times > target->backoff.count) {
-			/* do not poll this time as we failed previously */
-			target->backoff.count++;
-			continue;
+		/* polling may fail silently until the target has been examined */
+		retval = target_poll(target);
+		if (retval == ERROR_OK) {
+			target->backoff.interval = polling_interval;
+		} else {
+			/* Increase interval between polling up to 5000ms */
+			target->backoff.interval = MAX(polling_interval,
+					MIN(target->backoff.interval * 2 + 1, 5000));
+			/* Tell GDB to halt the debugger. This allows the user to run
+			* monitor commands to handle the situation. */
+			target_call_event_callbacks(target, TARGET_EVENT_GDB_HALT);
 		}
-		target->backoff.count = 0;
+		target->backoff.next_attempt = timeval_ms() + target->backoff.interval;
+		LOG_TARGET_DEBUG(target, "target_poll() -> %d, next attempt in %dms",
+				 retval, target->backoff.interval);
 
-		/* only poll target if we've got power and srst isn't asserted */
-		if (!power_dropout && !srst_asserted) {
-			/* polling may fail silently until the target has been examined */
-			retval = target_poll(target);
+		if (retval != ERROR_OK && examine_attempted) {
+			target_reset_examined(target);
+			retval = target_examine_one(target);
 			if (retval != ERROR_OK) {
-				/* 100ms polling interval. Increase interval between polling up to 5000ms */
-				if (target->backoff.times * polling_interval < 5000)
-					target->backoff.times = MIN(target->backoff.times * 2 + 1,
-												5000 / polling_interval);
-
-				/* Tell GDB to halt the debugger. This allows the user to
-				 * run monitor commands to handle the situation.
-				 */
-				target_call_event_callbacks(target, TARGET_EVENT_GDB_HALT);
-			}
-			if (target->backoff.times > 0 && examine_attempted) {
-				LOG_DEBUG("[%s] Polling failed, trying to reexamine", target_name(target));
-				target_reset_examined(target);
-				retval = target_examine_one(target);
-				if (retval != ERROR_OK) {
-					LOG_DEBUG("[%s] Examination failed, GDB will be halted. Polling again in %dms",
-						 target_name(target), target->backoff.times * polling_interval);
-					return retval;
-				}
+				LOG_TARGET_DEBUG(target, "Examination failed, GDB will be halted. "
+					"Polling again in %dms",
+					target->backoff.interval);
+				return retval;
 			}
-
-			/* Since we succeeded, we reset backoff count */
-			target->backoff.times = 0;
 		}
 	}
 
diff --git a/src/target/target.h b/src/target/target.h
index 4b494d8..726a14d 100644
--- a/src/target/target.h
+++ b/src/target/target.h
@@ -117,8 +117,8 @@ struct gdb_service {
 
 /* target back off timer */
 struct backoff_timer {
-	int times;
-	int count;
+	int64_t next_attempt;
+	unsigned int interval;
 };
 
 /* split target registers into multiple class */
@@ -199,6 +199,9 @@ struct target {
 	struct rtos *rtos;					/* Instance of Real Time Operating System support */
 	bool rtos_auto_detect;				/* A flag that indicates that the RTOS has been specified as "auto"
 										 * and must be detected when symbols are offered */
+	/* Track when next to poll(). If polling is failing, we don't want to
+	 * poll too quickly because we'll just overwhelm the user with error
+	 * messages. */
 	struct backoff_timer backoff;
 	int smp;							/* add some target attributes for smp support */
 	struct list_head *smp_targets;		/* list all targets in this smp group/cluster