[PATCH 6/8] drm/i915: Report whether we have true context isolation

[Chris Wilson]

Let userspace know if they can trust that new contexts are created using
HW default values; and avoid inheriting state from existing contexts.

Note: I intend to squash this into the bugfix once we agree on the uabi.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 11 +++++++++++
 include/uapi/drm/i915_drm.h     | 14 ++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 1b440f2b90a5..297b120e2aed 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -406,6 +406,17 @@ static int i915_getparam(struct drm_device *dev, void *data,
 		 */
 		value = 1;
 		break;
+	case I915_PARAM_HAS_CONTEXT_ISOLATION:
+		{
+			struct intel_engine_cs *engine;
+			enum intel_engine_id id;
+
+			value = 0;
+			for_each_engine(engine, dev_priv, id)
+				if (engine->context_size)
+					value |= BIT(engine->hw_id);
+		}
+		break;
 	case I915_PARAM_SLICE_MASK:
 		value = INTEL_INFO(dev_priv)->sseu.slice_mask;
 		if (!value)
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 125bde7d9504..ccecd7c16977 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -450,6 +450,20 @@ typedef struct drm_i915_irq_wait {
  */
 #define I915_PARAM_HAS_EXEC_FENCE_ARRAY  49
 
+/*
+ * Query whether every context (both per-file default and user created) is
+ * isolation (insofar as HW supports). If this parameter is not true, then
+ * freshly created contexts may inherit values from an existing context,
+ * rather than default HW values. If true, it also ensures (insofar as HW
+ * supports) that all state set by this context will not leak to any other
+ * context.
+ *
+ * As not every engine support contexts, the returned value reports the
+ * support of context isolation for individual engines by returning
+ * a bitmask of each HW ID set to true if that engine supports isolation.
+ */
+#define I915_PARAM_HAS_CONTEXT_ISOLATION 50
+
 typedef struct drm_i915_getparam {
 	__s32 param;
 	/*
-- 
2.15.0