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

[Mika Kuoppala]

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>
---
 drivers/gpu/drm/i915/i915_reg.h          | 1 +
 drivers/gpu/drm/i915/intel_uncore.c      | 2 ++
 drivers/gpu/drm/i915/intel_workarounds.c | 9 +++++++++
 3 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index f0317bde3aab..0e8c7896cd74 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2242,6 +2242,7 @@ enum i915_power_well_id {
 #define RING_RESET_CTL(base)	_MMIO((base)+0xd0)
 #define   RESET_CTL_REQUEST_RESET  (1 << 0)
 #define   RESET_CTL_READY_TO_RESET (1 << 1)
+#define RING_SEMA_WAIT_POLL(base) _MMIO((base)+0x24c)
 
 #define HSW_GTT_CACHE_EN	_MMIO(0x4024)
 #define   GTT_CACHE_EN_ALL	0xF0007FFF
diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index bb03f6d8b3d1..b892ca8396e8 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -2174,6 +2174,8 @@ int intel_gpu_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
 		 * Thus assume it is best to stop engines on all gens
 		 * where we have a gpu reset.
 		 *
+		 * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
+		 *
 		 * WaMediaResetMainRingCleanup:ctg,elk (presumably)
 		 *
 		 * FIXME: Wa for more modern gens needs to be validated
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)) {
+		struct intel_engine_cs *engine;
+		unsigned int tmp;
+
+		for_each_engine(engine, dev_priv, tmp)
+			I915_WRITE(RING_SEMA_WAIT_POLL(engine->mmio_base), 1);
+	}
 }
 
 static void glk_gt_workarounds_apply(struct drm_i915_private *dev_priv)
-- 
2.17.0