drm/sched: Add scheduler unit testing infrastructure and some basic tests

Implement a mock scheduler backend and add some basic test to exercise the
core scheduler code paths.

Mock backend (kind of like a very simple mock GPU) can either process jobs
by tests manually advancing the "timeline" job at a time, or alternatively
jobs can be configured with a time duration in which case they get
completed asynchronously from the unit test code.

Core scheduler classes are subclassed to support this mock implementation.

The tests added are just a few simple submission patterns.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Suggested-by: Philipp Stanner <phasta@kernel.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <phasta@kernel.org>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250324092633.49746-3-tvrtko.ursulin@igalia.com

drivers/gpu/drm/scheduler/tests/sched_tests.h

@@ -0,0 +1,224 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2025 Valve Corporation */
+
+#ifndef _SCHED_TESTS_H_
+#define _SCHED_TESTS_H_
+
+#include <kunit/test.h>
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/dma-fence.h>
+#include <linux/hrtimer.h>
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/atomic.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#include <drm/gpu_scheduler.h>
+
+/*
+ * DOC: Mock DRM scheduler data structures
+ *
+ * drm_mock_* data structures are used to implement a mock "GPU".
+ *
+ * They subclass the core DRM scheduler objects and add their data on top, which
+ * enables tracking the submitted jobs and simulating their execution with the
+ * attributes as specified by the test case.
+ */
+
+/**
+ * struct drm_mock_scheduler - implements a trivial mock GPU execution engine
+ *
+ * @base: DRM scheduler base class
+ * @test: Backpointer to owning the kunit test case
+ * @lock: Lock to protect the simulated @hw_timeline, @job_list and @done_list
+ * @job_list: List of jobs submitted to the mock GPU
+ * @done_list: List of jobs completed by the mock GPU
+ * @hw_timeline: Simulated hardware timeline has a @context, @next_seqno and
+ *		 @cur_seqno for implementing a struct dma_fence signaling the
+ *		 simulated job completion.
+ *
+ * Trivial mock GPU execution engine tracks submitted jobs and enables
+ * completing them strictly in submission order.
+ */
+struct drm_mock_scheduler {
+	struct drm_gpu_scheduler base;
+
+	struct kunit		*test;
+
+	spinlock_t		lock;
+	struct list_head	job_list;
+	struct list_head	done_list;
+
+	struct {
+		u64		context;
+		atomic_t	next_seqno;
+		unsigned int	cur_seqno;
+	} hw_timeline;
+};
+
+/**
+ * struct drm_mock_sched_entity - implements a mock GPU sched entity
+ *
+ * @base: DRM scheduler entity base class
+ * @test: Backpointer to owning the kunit test case
+ *
+ * Mock GPU sched entity is used by the test cases to submit jobs to the mock
+ * scheduler.
+ */
+struct drm_mock_sched_entity {
+	struct drm_sched_entity base;
+
+	struct kunit		*test;
+};
+
+/**
+ * struct drm_mock_sched_job - implements a mock GPU job
+ *
+ * @base: DRM sched job base class
+ * @done: Completion signaling job completion.
+ * @flags: Flags designating job state.
+ * @link: List head element used by job tracking by the drm_mock_scheduler
+ * @timer: Timer used for simulating job execution duration
+ * @duration_us: Simulated job duration in micro seconds, or zero if in manual
+ *		 timeline advance mode
+ * @finish_at: Absolute time when the jobs with set duration will complete
+ * @lock: Lock used for @hw_fence
+ * @hw_fence: Fence returned to DRM scheduler as the hardware fence
+ * @test: Backpointer to owning the kunit test case
+ *
+ * Mock GPU sched job is used by the test cases to submit jobs to the mock
+ * scheduler.
+ */
+struct drm_mock_sched_job {
+	struct drm_sched_job	base;
+
+	struct completion	done;
+
+#define DRM_MOCK_SCHED_JOB_DONE		0x1
+	unsigned long		flags;
+
+	struct list_head	link;
+	struct hrtimer		timer;
+
+	unsigned int		duration_us;
+	ktime_t			finish_at;
+
+	spinlock_t		lock;
+	struct dma_fence	hw_fence;
+
+	struct kunit		*test;
+};
+
+static inline struct drm_mock_scheduler *
+drm_sched_to_mock_sched(struct drm_gpu_scheduler *sched)
+{
+	return container_of(sched, struct drm_mock_scheduler, base);
+};
+
+static inline struct drm_mock_sched_entity *
+drm_sched_entity_to_mock_entity(struct drm_sched_entity *sched_entity)
+{
+	return container_of(sched_entity, struct drm_mock_sched_entity, base);
+};
+
+static inline struct drm_mock_sched_job *
+drm_sched_job_to_mock_job(struct drm_sched_job *sched_job)
+{
+	return container_of(sched_job, struct drm_mock_sched_job, base);
+};
+
+struct drm_mock_scheduler *drm_mock_sched_new(struct kunit *test);
+void drm_mock_sched_fini(struct drm_mock_scheduler *sched);
+unsigned int drm_mock_sched_advance(struct drm_mock_scheduler *sched,
+				    unsigned int num);
+
+struct drm_mock_sched_entity *
+drm_mock_sched_entity_new(struct kunit *test,
+			  enum drm_sched_priority priority,
+			  struct drm_mock_scheduler *sched);
+void drm_mock_sched_entity_free(struct drm_mock_sched_entity *entity);
+
+struct drm_mock_sched_job *
+drm_mock_sched_job_new(struct kunit *test,
+		       struct drm_mock_sched_entity *entity);
+
+/**
+ * drm_mock_sched_job_submit - Arm and submit a job in one go
+ *
+ * @job: Job to arm and submit
+ */
+static inline void drm_mock_sched_job_submit(struct drm_mock_sched_job *job)
+{
+	drm_sched_job_arm(&job->base);
+	drm_sched_entity_push_job(&job->base);
+}
+
+/**
+ * drm_mock_sched_job_set_duration_us - Set a job duration
+ *
+ * @job: Job to set the duration for
+ * @duration_us: Duration in micro seconds
+ *
+ * Jobs with duration set will be automatically completed by the mock scheduler
+ * as the timeline progresses, unless a job without a set duration is
+ * encountered in the timelime in which case calling drm_mock_sched_advance()
+ * will be required to bump the timeline.
+ */
+static inline void
+drm_mock_sched_job_set_duration_us(struct drm_mock_sched_job *job,
+				   unsigned int duration_us)
+{
+	job->duration_us = duration_us;
+}
+
+/**
+ * drm_mock_sched_job_is_finished - Check if a job is finished
+ *
+ * @job: Job to check
+ *
+ * Returns: true if finished
+ */
+static inline bool
+drm_mock_sched_job_is_finished(struct drm_mock_sched_job *job)
+{
+	return job->flags & DRM_MOCK_SCHED_JOB_DONE;
+}
+
+/**
+ * drm_mock_sched_job_wait_finished - Wait until a job is finished
+ *
+ * @job: Job to wait for
+ * @timeout: Wait time in jiffies
+ *
+ * Returns: true if finished within the timeout provided, otherwise false
+ */
+static inline bool
+drm_mock_sched_job_wait_finished(struct drm_mock_sched_job *job, long timeout)
+{
+	if (job->flags & DRM_MOCK_SCHED_JOB_DONE)
+		return true;
+
+	return wait_for_completion_timeout(&job->done, timeout) != 0;
+}
+
+/**
+ * drm_mock_sched_job_wait_scheduled - Wait until a job is scheduled
+ *
+ * @job: Job to wait for
+ * @timeout: Wait time in jiffies
+ *
+ * Returns: true if scheduled within the timeout provided, otherwise false
+ */
+static inline bool
+drm_mock_sched_job_wait_scheduled(struct drm_mock_sched_job *job, long timeout)
+{
+	KUNIT_ASSERT_EQ(job->test, job->flags & DRM_MOCK_SCHED_JOB_DONE, 0);
+
+	return dma_fence_wait_timeout(&job->base.s_fence->scheduled,
+				      false,
+				      timeout) != 0;
+}
+
+#endif