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    Subject[PATCH 4.11 059/197] drm/nouveau/tmr: avoid processing completed alarms when adding a new one
    Date
    4.11-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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

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