[Skiboot] [PATCH 09/11] hw/sbe-p9: Fix sbe_last_gen_stamp timing inconsistency

[Nicholas Piggin]

sbe_last_gen_stamp isn't a very clear name, so rename it to
sbe_current_timer_tb first of all. This is used to detect if
the timer should be programmed to get an earlier timeout.

One issue with it is that it is set *after* the SBE acks the
timer message, at which point the SBE could already have
started counting the timer. This means the SBE timer interrupt
could come in before that time, which is confusing and error
prone. Set the field at the point the timer is submitted to
the SBE.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 hw/sbe-p9.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/hw/sbe-p9.c b/hw/sbe-p9.c
index 6a0f76c5e..396da70ec 100644
--- a/hw/sbe-p9.c
+++ b/hw/sbe-p9.c
@@ -78,7 +78,7 @@ static bool sbe_timer_in_progress = false;
 static bool has_new_target = false;
 
 /* Inflight and next timer in TB */
-static uint64_t sbe_last_gen_stamp;
+static uint64_t sbe_current_timer_tb;
 static uint64_t sbe_timer_target;
 
 /* Timer lock */
@@ -695,7 +695,7 @@ static void p9_sbe_timer_poll(struct p9_sbe *sbe)
 	if (!sbe_timer_good || !sbe_timer_in_progress)
 		return;
 
-	if (tb_compare(mftb(), sbe_last_gen_stamp + msecs_to_tb(10))
+	if (tb_compare(mftb(), sbe_current_timer_tb + msecs_to_tb(10))
 	    != TB_AAFTERB)
 		return;
 
@@ -783,8 +783,6 @@ static void p9_sbe_timer_resp(struct p9_sbe_msg *msg)
 		      sbe_default_chip_id);
 	} else {
 		/* Update last scheduled timer value */
-		sbe_last_gen_stamp = mftb() +
-			usecs_to_tb(timer_ctrl_msg->reg[1]);
 		sbe_timer_in_progress = true;
 	}
 
@@ -812,14 +810,14 @@ static void p9_sbe_timer_schedule(void)
 		return;
 
 	if (sbe_timer_in_progress) {
-		if (sbe_timer_target >= sbe_last_gen_stamp)
+		if (sbe_timer_target >= sbe_current_timer_tb)
 			return;
 
-		if (now >= sbe_last_gen_stamp)
+		if (now >= sbe_current_timer_tb)
 			return;
 
 		/* Remaining time of inflight timer <= sbe_timer_min_tb */
-		if ((sbe_last_gen_stamp - now) <= sbe_timer_min_tb)
+		if ((sbe_current_timer_tb - now) <= sbe_timer_min_tb)
 			return;
 	}
 
@@ -831,6 +829,7 @@ static void p9_sbe_timer_schedule(void)
 			tick_us = tb_to_usecs(tb_cnt);
 		}
 	}
+	sbe_current_timer_tb = now + usecs_to_tb(tick_us);
 
 	/* Clear sequence number. p9_sbe_queue_msg will add new sequene ID */
 	timer_ctrl_msg->reg[0] &= ~(PPC_BITMASK(32, 47));
@@ -965,7 +964,7 @@ static void p9_sbe_timer_init(void)
 	sbe_has_timer = true;
 	sbe_timer_good = true;
 	sbe_timer_target = ~0ull;
-	sbe_last_gen_stamp = ~0ull;
+	sbe_current_timer_tb = ~0ull;
 	sbe_timer_min_us = SBE_TIMER_MIN_US_P9;
 	sbe_timer_min_tb = usecs_to_tb(sbe_timer_min_us);
 
-- 
2.45.2