Quoting Tvrtko Ursulin (2018-02-08 16:00:36)
> From: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
> We can implement limited RC6 counter wrap-around protection under the
> assumption that clients will be reading this value more frequently than
> the wrap period on a given platform.
> With the typical wrap-around period being ~90 minutes, even with the
> exception of Baytrail which wraps every 13 seconds, this sounds like a
> reasonable assumption.
> Implementation works by storing a 64-bit software copy of a hardware RC6
> counter, along with the previous HW counter snapshot. This enables it to
> detect wrap is polled frequently enough and keep the software copy
> monotonically incrementing.
> * Missed GEN6_GT_GFX_RC6_LOCKED when considering slot sizing and
> * Fixed off-by-one in wrap-around handling. (Chris Wilson)
> * Simplify index checking by using unsigned int. (Chris Wilson)
> * Expand the comment to explain why indexing works.
> * Use __int128 if supported.
> * Use mul_u64_u32_div. (Chris Wilson)
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94852
> Cc: Chris Wilson <ch...@chris-wilson.co.uk>
> Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk> # v3
> Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk>
Ville better not complain he liked the round up behaviour :-p
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