[Intel-gfx] [PATCH v5] drm/i915: Handle RC6 counter wrap

[Ville Syrjälä]

On Tue, Feb 13, 2018 at 02:09:51PM +0000, Tvrtko Ursulin wrote:
> 
> On 08/02/2018 16:04, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-02-08 16:00:36)
> >> From: Tvrtko Ursulin <tvrtko.ursulin at 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.ursulin at intel.com>
> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94852
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> # v3
> >> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> > 
> > Ville better not complain he liked the round up behaviour :-p
> 
> Ping Ville - ack?

ack

-- 
Ville Syrjälä
Intel OTC