Patch "drm/nouveau/tmr: avoid processing completed alarms when adding a new one" has been added to the 4.4-stable tree

Patch "drm/nouveau/tmr: avoid processing completed alarms when adding a new one" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    drm/nouveau/tmr: avoid processing completed alarms when adding a new one

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-nouveau-tmr-avoid-processing-completed-alarms-when-adding-a-new-one.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 330bdf62fe6a6c5b99a647f7bf7157107c9348b3 Mon Sep 17 00:00:00 2001
From: Ben Skeggs <bskeggs@redhat.com>
Date: Thu, 11 May 2017 17:13:29 +1000
Subject: drm/nouveau/tmr: avoid processing completed alarms when adding a new one

From: Ben Skeggs <bskeggs@redhat.com>

commit 330bdf62fe6a6c5b99a647f7bf7157107c9348b3 upstream.

The idea here was to avoid having to "manually" program the HW if there's
a new earliest alarm.  This was lazy and bad, as it leads to loads of fun
races between inter-related callers (ie. therm).

Turns out, it's not so difficult after all.  Go figure ;)

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
@@ -80,12 +80,22 @@ nvkm_timer_alarm(struct nvkm_timer *tmr,
 			if (list->timestamp > alarm->timestamp)
 				break;
 		}
+
 		list_add_tail(&alarm->head, &list->head);
+
+		/* Update HW if this is now the earliest alarm. */
+		list = list_first_entry(&tmr->alarms, typeof(*list), head);
+		if (list == alarm) {
+			tmr->func->alarm_init(tmr, alarm->timestamp);
+			/* This shouldn't happen if callers aren't stupid.
+			 *
+			 * Worst case scenario is that it'll take roughly
+			 * 4 seconds for the next alarm to trigger.
+			 */
+			WARN_ON(alarm->timestamp <= nvkm_timer_read(tmr));
+		}
 	}
 	spin_unlock_irqrestore(&tmr->lock, flags);
-
-	/* process pending alarms */
-	nvkm_timer_alarm_trigger(tmr);
 }
 
 void


Patches currently in stable-queue which might be from bskeggs@redhat.com are

queue-4.4/drm-nouveau-tmr-ack-interrupt-before-processing-alarms.patch
queue-4.4/drm-nouveau-tmr-fix-corruption-of-the-pending-list-when-rescheduling-an-alarm.patch
queue-4.4/drm-nouveau-tmr-avoid-processing-completed-alarms-when-adding-a-new-one.patch
queue-4.4/drm-nouveau-mmu-nv4a-use-nv04-mmu-rather-than-the-nv44-one.patch
queue-4.4/drm-nouveau-therm-remove-ineffective-workarounds-for-alarm-bugs.patch
queue-4.4/drm-nouveau-tmr-handle-races-with-hw-when-updating-the-next-alarm-time.patch