[Intel-gfx] [PATCH 2/2] drm/i915: Add WaKBLVECSSemaphoreWaitPoll

[Chris Wilson]

Quoting Mika Kuoppala (2018-06-05 17:03:57)
> There is a problem with kbl up to rev E0 where a heavy
> memory/fabric traffic from adjacent engine(s) can cause an engine
> reset to fail. This traffic can be from normal memory accesses
> or it can be from heavy polling on a semaphore wait.
> 
> For engine hogging causing a fail, we already fallback to
> full reset. Which effectively stops all engines and thus
> we only add a workaround documentation.
> 
> For the semaphore wait loop poll case, we add one microsecond
> poll interval to semaphore wait to guarantee bandwidth for
> the reset preration. The side effect is that we make semaphore
> completion latencies also 1us longer.
> 
> v2: Let full reset handle the adjacent engine idling (Chris)
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=106684
> References: VTHSD#2227190, HSDES#1604216706, BSID#0917
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
> diff --git a/drivers/gpu/drm/i915/intel_workarounds.c b/drivers/gpu/drm/i915/intel_workarounds.c
> index b1ab56a1ec31..5655d39c65cb 100644
> --- a/drivers/gpu/drm/i915/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/intel_workarounds.c
> @@ -666,6 +666,15 @@ static void kbl_gt_workarounds_apply(struct drm_i915_private *dev_priv)
>         I915_WRITE(GEN9_GAMT_ECO_REG_RW_IA,
>                    I915_READ(GEN9_GAMT_ECO_REG_RW_IA) |
>                    GAMT_ECO_ENABLE_IN_PLACE_DECOMPRESS);
> +
> +       /* WaKBLVECSSemaphoreWaitPoll:kbl */
> +       if (IS_KBL_REVID(dev_priv, KBL_REVID_A0, KBL_REVID_E0)) {

Hmm, what revision was production? Just checking we need to ship this
w/a...
-Chris