On gen7, we have to avoid concurrent access to the same mmio cacheline,
and so coordinate all mmio access with the uncore->lock. However, for
pmu, we want to avoid perturbing the system and disabling interrupts
unnecessarily, so restrict the w/a to gen7 where it is requied to
prevent machine hangs.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_pmu.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 8e74f40413b8..4804775644bf 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -292,6 +292,16 @@ add_sample(struct i915_pmu_sample *sample, u32 val)
sample->cur += val;
}
+static bool exclusive_mmio_access(const struct drm_i915_private *i915)
+{
+ /*
+ * We have to avoid concurrent mmio cache line access on gen7 or
+ * risk a machine hang. For a fun history lesson dig out the old
+ * userspace intel_gpu_top and run it on Ivybridge or Haswell!
+ */
+ return IS_GEN(i915, 7);
+}
+
static void
engines_sample(struct intel_gt *gt, unsigned int period_ns)
{
@@ -304,6 +314,7 @@ engines_sample(struct intel_gt *gt, unsigned int period_ns)
for_each_engine(engine, gt, id) {
struct intel_engine_pmu *pmu = &engine->pmu;
+ spinlock_t *mmio_lock;
unsigned long flags;
bool busy;
u32 val;
@@ -311,7 +322,12 @@ engines_sample(struct intel_gt *gt, unsigned int period_ns)
if (!intel_engine_pm_get_if_awake(engine))
continue;
- spin_lock_irqsave(&engine->uncore->lock, flags);
+ mmio_lock = NULL;
+ if (exclusive_mmio_access(i915))
+ mmio_lock = &engine->uncore->lock;
+
+ if (unlikely(mmio_lock))
+ spin_lock_irqsave(mmio_lock, flags);
val = ENGINE_READ_FW(engine, RING_CTL);
if (val == 0) /* powerwell off => engine idle */
@@ -342,7 +358,8 @@ engines_sample(struct intel_gt *gt, unsigned int period_ns)
add_sample(&pmu->sample[I915_SAMPLE_BUSY], period_ns);
skip:
- spin_unlock_irqrestore(&engine->uncore->lock, flags);
+ if (unlikely(mmio_lock))
+ spin_unlock_irqrestore(mmio_lock, flags);
intel_engine_pm_put(engine);
}
}
--
2.24.0
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