On 08/02/2018 16:04, Chris Wilson wrote:
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.

v2:
  * Missed GEN6_GT_GFX_RC6_LOCKED when considering slot sizing and
    indexing.
  * Fixed off-by-one in wrap-around handling. (Chris Wilson)

v3:
  * Simplify index checking by using unsigned int. (Chris Wilson)
  * Expand the comment to explain why indexing works.

v4:
  * Use __int128 if supported.

v5:
  * 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

Ping Ville - ack?

Regards,

Tvrtko

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