On 24/03/16 13:42, Chris Wilson wrote:
On Thu, Mar 24, 2016 at 01:32:53PM +0000, Chris Wilson wrote:
If we arm the release timer on acquiring the forcewake, we will release
the forcewake on the jiffie afterwards. If we only arm the release timer
on the final put, we will release the forcewake slightly later instead.
Much, much worse, we did not acquire a refcount for the armed timing
during the get(), and so unbalanced our forcewake counting.
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_uncore.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 96799392c2c7..d857168c6c9b 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -60,6 +60,7 @@ fw_domain_reset(const struct intel_uncore_forcewake_domain *d)
static inline void
fw_domain_arm_timer(struct intel_uncore_forcewake_domain *d)
{
+ d->wake_count++;
mod_timer_pinned(&d->timer, jiffies + 1);
Which raise the obvious issue that we double increment the counter if
the timer was pending (where we would only then release it once).
I don't see the bug, we got:
1) __intel_uncore_forcewake_put - if refcount reaches zero it will bump
it and arm the timer to decrement and release. This is used from
explicit get/put paths.
2) __force_wake_get - used from register reads only, so no explicit put
will happen. It just bumps the ref count and arms the timer.
I can't spot the bug, if there is one.
Regards,
Tvrtko
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