[PATCH 37/40] drm/i915: Allow a context to define its set of engines

[Chris Wilson <chris@chris-wilson.co.uk>]

Over the last few years, we have debated how to extend the user API to
support an increase in the number of engines, that may be sparse and
even be heterogeneous within a class (not all video decoders created
equal). We settled on using (class, instance) tuples to identify a
specific engine, with an API for the user to construct a map of engines
to capabilities. Into this picture, we then add a challenge of virtual
engines; one user engine that maps behind the scenes to any number of
physical engines. To keep it general, we want the user to have full
control over that mapping. To that end, we allow the user to constrain a
context to define the set of engines that it can access, order fully
controlled by the user via (class, instance). With such precise control
in context setup, we can continue to use the existing execbuf uABI of
specifying a single index; only now it doesn't automagically map onto
the engines, it uses the user defined engine map from the context.

The I915_EXEC_DEFAULT slot is left empty, and invalid for use by
execbuf. It's use will be revealed in the next patch.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_context.c    | 88 ++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_context.h    |  4 +
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 22 ++++--
 include/uapi/drm/i915_drm.h                | 27 +++++++
 4 files changed, 135 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index a8570a07b3b7..313471253f51 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -90,6 +90,7 @@
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
 #include "i915_trace.h"
+#include "i915_user_extensions.h"
 #include "intel_workarounds.h"
 
 #define ALL_L3_SLICES(dev) (1 << NUM_L3_SLICES(dev)) - 1
@@ -223,6 +224,8 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
 			ce->ops->destroy(ce);
 	}
 
+	kfree(ctx->engines);
+
 	if (ctx->timeline)
 		i915_timeline_put(ctx->timeline);
 
@@ -948,6 +951,87 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
 	return ret;
 }
 
+struct set_engines {
+	struct i915_gem_context *ctx;
+	struct intel_engine_cs **engines;
+	unsigned int nengine;
+};
+
+static const i915_user_extension_fn set_engines__extensions[] = {
+};
+
+static int set_engines(struct i915_gem_context *ctx,
+		       struct drm_i915_gem_context_param *args)
+{
+	struct i915_context_param_engines __user *user;
+	struct set_engines set = {
+		.ctx = ctx,
+		.engines = NULL,
+		.nengine = -1,
+	};
+	unsigned int n;
+	u64 size, extensions;
+	int err;
+
+	user = u64_to_user_ptr(args->value);
+	size = args->size;
+	if (!size)
+		goto out;
+
+	if (size < sizeof(struct i915_context_param_engines))
+		return -EINVAL;
+
+	size -= sizeof(struct i915_context_param_engines);
+	if (size % sizeof(*user->class_instance))
+		return -EINVAL;
+
+	set.nengine = size / sizeof(*user->class_instance);
+	if (set.nengine == 0 || set.nengine >= I915_EXEC_RING_MASK)
+		return -EINVAL;
+
+	set.engines = kmalloc_array(set.nengine + 1,
+				    sizeof(*set.engines),
+				    GFP_KERNEL);
+	if (!set.engines)
+		return -ENOMEM;
+
+	set.engines[0] = NULL;
+	for (n = 0; n < set.nengine; n++) {
+		u32 class, instance;
+
+		if (get_user(class, &user->class_instance[n].class) ||
+		    get_user(instance, &user->class_instance[n].instance)) {
+			kfree(set.engines);
+			return -EFAULT;
+		}
+
+		set.engines[n + 1] =
+			intel_engine_lookup_user(ctx->i915, class, instance);
+		if (!set.engines[n + 1]) {
+			kfree(set.engines);
+			return -ENOENT;
+		}
+	}
+
+	err = -EFAULT;
+	if (!get_user(extensions, &user->extensions))
+		err = i915_user_extensions(u64_to_user_ptr(extensions),
+					   set_engines__extensions,
+					   ARRAY_SIZE(set_engines__extensions),
+					   &set);
+	if (err) {
+		kfree(set.engines);
+		return err;
+	}
+
+out:
+	kfree(ctx->engines);
+	ctx->engines = set.engines;
+	ctx->nengine = set.nengine + 1;
+
+	return 0;
+}
+
 int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 				    struct drm_file *file)
 {
@@ -1011,6 +1095,10 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
 		}
 		break;
 
+	case I915_CONTEXT_PARAM_ENGINES:
+		ret = set_engines(ctx, args);
+		break;
+
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/drivers/gpu/drm/i915/i915_gem_context.h b/drivers/gpu/drm/i915/i915_gem_context.h
index 770043449ba6..9f89119a6566 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.h
+++ b/drivers/gpu/drm/i915/i915_gem_context.h
@@ -67,6 +67,8 @@ struct i915_gem_context {
 	/** file_priv: owning file descriptor */
 	struct drm_i915_file_private *file_priv;
 
+	struct intel_engine_cs **engines;
+
 	struct i915_timeline *timeline;
 
 	/**
@@ -135,6 +137,8 @@ struct i915_gem_context {
 #define CONTEXT_CLOSED			1
 #define CONTEXT_FORCE_SINGLE_SUBMISSION	2
 
+	unsigned int nengine;
+
 	/**
 	 * @hw_id: - unique identifier for the context
 	 *
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 109486a6ef07..faedfdca875d 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -2014,13 +2014,23 @@ static const enum intel_engine_id user_ring_map[I915_USER_RINGS + 1] = {
 };
 
 static struct intel_engine_cs *
-eb_select_engine(struct drm_i915_private *dev_priv,
+eb_select_engine(struct i915_execbuffer *eb,
 		 struct drm_file *file,
 		 struct drm_i915_gem_execbuffer2 *args)
 {
 	unsigned int user_ring_id = args->flags & I915_EXEC_RING_MASK;
 	struct intel_engine_cs *engine;
 
+	if (eb->ctx->engines) {
+		if (user_ring_id >= eb->ctx->nengine) {
+			DRM_DEBUG("execbuf with unknown ring: %u\n",
+				  user_ring_id);
+			return NULL;
+		}
+
+		return eb->ctx->engines[user_ring_id];
+	}
+
 	if (user_ring_id > I915_USER_RINGS) {
 		DRM_DEBUG("execbuf with unknown ring: %u\n", user_ring_id);
 		return NULL;
@@ -2033,11 +2043,11 @@ eb_select_engine(struct drm_i915_private *dev_priv,
 		return NULL;
 	}
 
-	if (user_ring_id == I915_EXEC_BSD && HAS_BSD2(dev_priv)) {
+	if (user_ring_id == I915_EXEC_BSD && HAS_BSD2(eb->i915)) {
 		unsigned int bsd_idx = args->flags & I915_EXEC_BSD_MASK;
 
 		if (bsd_idx == I915_EXEC_BSD_DEFAULT) {
-			bsd_idx = gen8_dispatch_bsd_engine(dev_priv, file);
+			bsd_idx = gen8_dispatch_bsd_engine(eb->i915, file);
 		} else if (bsd_idx >= I915_EXEC_BSD_RING1 &&
 			   bsd_idx <= I915_EXEC_BSD_RING2) {
 			bsd_idx >>= I915_EXEC_BSD_SHIFT;
@@ -2048,9 +2058,9 @@ eb_select_engine(struct drm_i915_private *dev_priv,
 			return NULL;
 		}
 
-		engine = dev_priv->engine[_VCS(bsd_idx)];
+		engine = eb->i915->engine[_VCS(bsd_idx)];
 	} else {
-		engine = dev_priv->engine[user_ring_map[user_ring_id]];
+		engine = eb->i915->engine[user_ring_map[user_ring_id]];
 	}
 
 	if (!engine) {
@@ -2260,7 +2270,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 	if (unlikely(err))
 		goto err_destroy;
 
-	eb.engine = eb_select_engine(eb.i915, file, args);
+	eb.engine = eb_select_engine(&eb, file, args);
 	if (!eb.engine) {
 		err = -EINVAL;
 		goto err_engine;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 65b0b84419f3..d41b4c673af4 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1508,9 +1508,36 @@ struct drm_i915_gem_context_param {
 #define   I915_CONTEXT_MAX_USER_PRIORITY	1023 /* inclusive */
 #define   I915_CONTEXT_DEFAULT_PRIORITY		0
 #define   I915_CONTEXT_MIN_USER_PRIORITY	-1023 /* inclusive */
+
+/*
+ * I915_CONTEXT_PARAM_ENGINES:
+ *
+ * Bind this context to operate on this subset of available engines. Henceforth,
+ * the I915_EXEC_RING selector for DRM_IOCTL_I915_GEM_EXECBUFFER2 operates as
+ * an index into this array of engines; I915_EXEC_DEFAULT selecting engine[0]
+ * and upwards. The array created is offset by 1, such that by default
+ * I915_EXEC_DEFAULT is left empty, to be filled in as directed. Slots 1...N
+ * are then filled in using the specified (class, instance).
+ *
+ * Setting the number of engines bound to the context will revert back to
+ * default settings.
+ *
+ * See struct i915_context_param_engines.
+ */
+#define I915_CONTEXT_PARAM_ENGINES	0x7
+
 	__u64 value;
 };
 
+struct i915_context_param_engines {
+	__u64 extensions;
+
+	struct {
+		__u32 class; /* see enum drm_i915_gem_engine_class */
+		__u32 instance;
+	} class_instance[0];
+};
+
 enum drm_i915_oa_format {
 	I915_OA_FORMAT_A13 = 1,	    /* HSW only */
 	I915_OA_FORMAT_A29,	    /* HSW only */
-- 
2.19.0

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