[Intel-gfx] [PATCH] drm/i915: Only arm the forcewake release timer on the final put

[Chris Wilson]

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 at linux.intel.com>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> ---
>  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).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre