[RFC v2] drm/i915: Engine discovery query

[Tvrtko Ursulin <tursulin@ursulin.net>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Engine discovery query allows userspace to enumerate engines, probe their
configuration features, all without needing to maintain the internal PCI
ID based database.

A new query for the generic i915 query ioctl is added named
DRM_I915_QUERY_ENGINE_INFO, together with accompanying structure
drm_i915_query_engine_info. The address of latter should be passed to the
kernel in the query.data_ptr field, and should be large enough for the
kernel to fill out all known engines as struct drm_i915_engine_info
elements trailing the query.

As with other queries, setting the item query length to zero allows
userspace to query minimum required buffer size.

Enumerated engines have common type mask which can be used to query all
hardware engines, versus engines userspace can submit to using the execbuf
uAPI.

Engines also have capabilities which are per engine class namespace of
bits describing features not present on all engine instances.

v2:
 * Fixed HEVC assignment.
 * Reorder some fields, rename type to flags, increase width. (Lionel)
 * No need to allocate temporary storage if we do it engine by engine.
   (Lionel)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
This is RFC for now since it is not very usable before the new execbuf API
or virtual engine queue submission gets closer.

In this version I have added capability of distinguishing between hardware
engines and ABI engines. This is to account for probable future use cases
like virtualization, where guest might only see one engine instance, but
will want to know overall hardware capabilities in order to tune its
behaviour.

In general I think we will have to wait a bit before defining the final
look of the uAPI, but in the meantime I thought it useful to share as RFC.
---
 drivers/gpu/drm/i915/i915_query.c       | 63 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_engine_cs.c  |  2 ++
 drivers/gpu/drm/i915/intel_ringbuffer.h |  3 ++
 include/uapi/drm/i915_drm.h             | 46 ++++++++++++++++++++++++
 4 files changed, 114 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
index 3ace929dd90f..a1c0e3acc882 100644
--- a/drivers/gpu/drm/i915/i915_query.c
+++ b/drivers/gpu/drm/i915/i915_query.c
@@ -82,9 +82,72 @@ static int query_topology_info(struct drm_i915_private *dev_priv,
 	return total_length;
 }
 
+static int
+query_engine_info(struct drm_i915_private *i915,
+		  struct drm_i915_query_item *query_item)
+{
+	struct drm_i915_query_engine_info __user *query_ptr =
+				u64_to_user_ptr(query_item->data_ptr);
+	struct drm_i915_engine_info __user *info_ptr = &query_ptr->engines[0];
+	struct drm_i915_query_engine_info query;
+	struct intel_engine_cs *engine;
+	enum intel_engine_id id;
+	int len;
+
+	if (query_item->flags)
+		return -EINVAL;
+
+	len = sizeof(struct drm_i915_query_engine_info) +
+	      I915_NUM_ENGINES * sizeof(struct drm_i915_engine_info);
+
+	if (!query_item->length)
+		return len;
+	else if (query_item->length < len)
+		return -EINVAL;
+
+	if (copy_from_user(&query, query_ptr, sizeof(query)))
+		return -EFAULT;
+
+	if (query.num_engines || query.rsvd[0] || query.rsvd[1] ||
+	    query.rsvd[2])
+		return -EINVAL;
+
+	if (!access_ok(VERIFY_WRITE, query_ptr, query_item->length))
+		return -EFAULT;
+
+	for_each_engine(engine, i915, id) {
+		struct drm_i915_engine_info info;
+
+		if (__copy_from_user(&info, info_ptr, sizeof(info)))
+			return -EFAULT;
+
+		if (info.flags || info.class || info.instance ||
+		    info.capabilities || info.rsvd0 || info.rsvd1[0] ||
+		    info.rsvd1[1])
+			return -EINVAL;
+
+		info.class = engine->uabi_class;
+		info.instance = engine->instance;
+		info.flags = I915_ENGINE_FLAG_PHYSICAL | I915_ENGINE_FLAG_ABI;
+		info.capabilities = engine->capabilities;
+
+		if (__copy_to_user(info_ptr, &info, sizeof(info)))
+			return -EFAULT;
+
+		query.num_engines++;
+		info_ptr++;
+	}
+
+	if (__copy_to_user(query_ptr, &query, sizeof(query)))
+		return -EFAULT;
+
+	return len;
+}
+
 static int (* const i915_query_funcs[])(struct drm_i915_private *dev_priv,
 					struct drm_i915_query_item *query_item) = {
 	query_topology_info,
+	query_engine_info,
 };
 
 int i915_query_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 12486d8f534b..9d26c34dfec4 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -294,6 +294,8 @@ intel_engine_setup(struct drm_i915_private *dev_priv,
 	engine->mmio_base = __engine_mmio_base(dev_priv, info->mmio_bases);
 	engine->class = info->class;
 	engine->instance = info->instance;
+	if (INTEL_GEN(dev_priv) >= 8 && info->instance == 0)
+		engine->capabilities = I915_VCS_CLASS_CAPABILITY_HEVC;
 
 	engine->uabi_id = info->uabi_id;
 	engine->uabi_class = intel_engine_classes[info->class].uabi_class;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 256d58487559..b23be52fc882 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -330,6 +330,9 @@ struct intel_engine_cs {
 
 	u8 class;
 	u8 instance;
+
+	u32 capabilities;
+
 	u32 context_size;
 	u32 mmio_base;
 
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 7f5634ce8e88..2eafb677cd40 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1620,6 +1620,7 @@ struct drm_i915_perf_oa_config {
 struct drm_i915_query_item {
 	__u64 query_id;
 #define DRM_I915_QUERY_TOPOLOGY_INFO    1
+#define DRM_I915_QUERY_ENGINE_INFO	2
 
 	/*
 	 * When set to zero by userspace, this is filled with the size of the
@@ -1717,6 +1718,51 @@ struct drm_i915_query_topology_info {
 	__u8 data[];
 };
 
+/**
+ * struct drm_i915_engine_info
+ *
+ * Describes one engine known to the driver, whether or not is physical engine
+ * only, or it can also be targetted from userspace, and what are its
+ * capabilities where applicable.
+ */
+struct drm_i915_engine_info {
+	/** Engine flags. */
+	__u64 flags;
+#define I915_ENGINE_FLAG_PHYSICAL	(1 << 0)
+#define I915_ENGINE_FLAG_ABI		(1 << 1)
+
+	/** Engine class as in enum drm_i915_gem_engine_class. */
+	__u16 class;
+
+	/** Engine instance number. */
+	__u16 instance;
+
+	__u32 rsvd0;
+
+	/** Capabilities of this engine. */
+	__u64 capabilities;
+#define I915_VCS_CLASS_CAPABILITY_HEVC	(1 << 0)
+
+	__u64 rsvd1[2];
+};
+
+/**
+ * struct drm_i915_query_engine_info
+ *
+ * Engine info query enumerates all the engines known to the driver returning
+ * the array of struct drm_i915_engine_info structures.
+ */
+struct drm_i915_query_engine_info {
+	/** Number of struct drm_i915_engine_info structs following. */
+	__u32 num_engines;
+
+	/** MBZ */
+	__u32 rsvd[3];
+
+	/** Marker for drm_i915_engine_info structures. */
+	struct drm_i915_engine_info engines[];
+};
+
 #if defined(__cplusplus)
 }
 #endif
-- 
2.14.1

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