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-rw-r--r--drivers/gpu/drm/i915/i915_active.h425
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diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
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index 000000000000..12b5c1d287d1
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+++ b/drivers/gpu/drm/i915/i915_active.h
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+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2019 Intel Corporation
+ */
+
+#ifndef _I915_ACTIVE_H_
+#define _I915_ACTIVE_H_
+
+#include <linux/lockdep.h>
+
+#include "i915_active_types.h"
+#include "i915_request.h"
+
+/*
+ * We treat requests as fences. This is not be to confused with our
+ * "fence registers" but pipeline synchronisation objects ala GL_ARB_sync.
+ * We use the fences to synchronize access from the CPU with activity on the
+ * GPU, for example, we should not rewrite an object's PTE whilst the GPU
+ * is reading them. We also track fences at a higher level to provide
+ * implicit synchronisation around GEM objects, e.g. set-domain will wait
+ * for outstanding GPU rendering before marking the object ready for CPU
+ * access, or a pageflip will wait until the GPU is complete before showing
+ * the frame on the scanout.
+ *
+ * In order to use a fence, the object must track the fence it needs to
+ * serialise with. For example, GEM objects want to track both read and
+ * write access so that we can perform concurrent read operations between
+ * the CPU and GPU engines, as well as waiting for all rendering to
+ * complete, or waiting for the last GPU user of a "fence register". The
+ * object then embeds a #i915_active_request to track the most recent (in
+ * retirement order) request relevant for the desired mode of access.
+ * The #i915_active_request is updated with i915_active_request_set() to
+ * track the most recent fence request, typically this is done as part of
+ * i915_vma_move_to_active().
+ *
+ * When the #i915_active_request completes (is retired), it will
+ * signal its completion to the owner through a callback as well as mark
+ * itself as idle (i915_active_request.request == NULL). The owner
+ * can then perform any action, such as delayed freeing of an active
+ * resource including itself.
+ */
+
+void i915_active_retire_noop(struct i915_active_request *active,
+ struct i915_request *request);
+
+/**
+ * i915_active_request_init - prepares the activity tracker for use
+ * @active - the active tracker
+ * @rq - initial request to track, can be NULL
+ * @func - a callback when then the tracker is retired (becomes idle),
+ * can be NULL
+ *
+ * i915_active_request_init() prepares the embedded @active struct for use as
+ * an activity tracker, that is for tracking the last known active request
+ * associated with it. When the last request becomes idle, when it is retired
+ * after completion, the optional callback @func is invoked.
+ */
+static inline void
+i915_active_request_init(struct i915_active_request *active,
+ struct i915_request *rq,
+ i915_active_retire_fn retire)
+{
+ RCU_INIT_POINTER(active->request, rq);
+ INIT_LIST_HEAD(&active->link);
+ active->retire = retire ?: i915_active_retire_noop;
+}
+
+#define INIT_ACTIVE_REQUEST(name) i915_active_request_init((name), NULL, NULL)
+
+/**
+ * i915_active_request_set - updates the tracker to watch the current request
+ * @active - the active tracker
+ * @request - the request to watch
+ *
+ * __i915_active_request_set() watches the given @request for completion. Whilst
+ * that @request is busy, the @active reports busy. When that @request is
+ * retired, the @active tracker is updated to report idle.
+ */
+static inline void
+__i915_active_request_set(struct i915_active_request *active,
+ struct i915_request *request)
+{
+ list_move(&active->link, &request->active_list);
+ rcu_assign_pointer(active->request, request);
+}
+
+int __must_check
+i915_active_request_set(struct i915_active_request *active,
+ struct i915_request *rq);
+
+/**
+ * i915_active_request_set_retire_fn - updates the retirement callback
+ * @active - the active tracker
+ * @fn - the routine called when the request is retired
+ * @mutex - struct_mutex used to guard retirements
+ *
+ * i915_active_request_set_retire_fn() updates the function pointer that
+ * is called when the final request associated with the @active tracker
+ * is retired.
+ */
+static inline void
+i915_active_request_set_retire_fn(struct i915_active_request *active,
+ i915_active_retire_fn fn,
+ struct mutex *mutex)
+{
+ lockdep_assert_held(mutex);
+ active->retire = fn ?: i915_active_retire_noop;
+}
+
+static inline struct i915_request *
+__i915_active_request_peek(const struct i915_active_request *active)
+{
+ /*
+ * Inside the error capture (running with the driver in an unknown
+ * state), we want to bend the rules slightly (a lot).
+ *
+ * Work is in progress to make it safer, in the meantime this keeps
+ * the known issue from spamming the logs.
+ */
+ return rcu_dereference_protected(active->request, 1);
+}
+
+/**
+ * i915_active_request_raw - return the active request
+ * @active - the active tracker
+ *
+ * i915_active_request_raw() returns the current request being tracked, or NULL.
+ * It does not obtain a reference on the request for the caller, so the caller
+ * must hold struct_mutex.
+ */
+static inline struct i915_request *
+i915_active_request_raw(const struct i915_active_request *active,
+ struct mutex *mutex)
+{
+ return rcu_dereference_protected(active->request,
+ lockdep_is_held(mutex));
+}
+
+/**
+ * i915_active_request_peek - report the active request being monitored
+ * @active - the active tracker
+ *
+ * i915_active_request_peek() returns the current request being tracked if
+ * still active, or NULL. It does not obtain a reference on the request
+ * for the caller, so the caller must hold struct_mutex.
+ */
+static inline struct i915_request *
+i915_active_request_peek(const struct i915_active_request *active,
+ struct mutex *mutex)
+{
+ struct i915_request *request;
+
+ request = i915_active_request_raw(active, mutex);
+ if (!request || i915_request_completed(request))
+ return NULL;
+
+ return request;
+}
+
+/**
+ * i915_active_request_get - return a reference to the active request
+ * @active - the active tracker
+ *
+ * i915_active_request_get() returns a reference to the active request, or NULL
+ * if the active tracker is idle. The caller must hold struct_mutex.
+ */
+static inline struct i915_request *
+i915_active_request_get(const struct i915_active_request *active,
+ struct mutex *mutex)
+{
+ return i915_request_get(i915_active_request_peek(active, mutex));
+}
+
+/**
+ * __i915_active_request_get_rcu - return a reference to the active request
+ * @active - the active tracker
+ *
+ * __i915_active_request_get() returns a reference to the active request,
+ * or NULL if the active tracker is idle. The caller must hold the RCU read
+ * lock, but the returned pointer is safe to use outside of RCU.
+ */
+static inline struct i915_request *
+__i915_active_request_get_rcu(const struct i915_active_request *active)
+{
+ /*
+ * Performing a lockless retrieval of the active request is super
+ * tricky. SLAB_TYPESAFE_BY_RCU merely guarantees that the backing
+ * slab of request objects will not be freed whilst we hold the
+ * RCU read lock. It does not guarantee that the request itself
+ * will not be freed and then *reused*. Viz,
+ *
+ * Thread A Thread B
+ *
+ * rq = active.request
+ * retire(rq) -> free(rq);
+ * (rq is now first on the slab freelist)
+ * active.request = NULL
+ *
+ * rq = new submission on a new object
+ * ref(rq)
+ *
+ * To prevent the request from being reused whilst the caller
+ * uses it, we take a reference like normal. Whilst acquiring
+ * the reference we check that it is not in a destroyed state
+ * (refcnt == 0). That prevents the request being reallocated
+ * whilst the caller holds on to it. To check that the request
+ * was not reallocated as we acquired the reference we have to
+ * check that our request remains the active request across
+ * the lookup, in the same manner as a seqlock. The visibility
+ * of the pointer versus the reference counting is controlled
+ * by using RCU barriers (rcu_dereference and rcu_assign_pointer).
+ *
+ * In the middle of all that, we inspect whether the request is
+ * complete. Retiring is lazy so the request may be completed long
+ * before the active tracker is updated. Querying whether the
+ * request is complete is far cheaper (as it involves no locked
+ * instructions setting cachelines to exclusive) than acquiring
+ * the reference, so we do it first. The RCU read lock ensures the
+ * pointer dereference is valid, but does not ensure that the
+ * seqno nor HWS is the right one! However, if the request was
+ * reallocated, that means the active tracker's request was complete.
+ * If the new request is also complete, then both are and we can
+ * just report the active tracker is idle. If the new request is
+ * incomplete, then we acquire a reference on it and check that
+ * it remained the active request.
+ *
+ * It is then imperative that we do not zero the request on
+ * reallocation, so that we can chase the dangling pointers!
+ * See i915_request_alloc().
+ */
+ do {
+ struct i915_request *request;
+
+ request = rcu_dereference(active->request);
+ if (!request || i915_request_completed(request))
+ return NULL;
+
+ /*
+ * An especially silly compiler could decide to recompute the
+ * result of i915_request_completed, more specifically
+ * re-emit the load for request->fence.seqno. A race would catch
+ * a later seqno value, which could flip the result from true to
+ * false. Which means part of the instructions below might not
+ * be executed, while later on instructions are executed. Due to
+ * barriers within the refcounting the inconsistency can't reach
+ * past the call to i915_request_get_rcu, but not executing
+ * that while still executing i915_request_put() creates
+ * havoc enough. Prevent this with a compiler barrier.
+ */
+ barrier();
+
+ request = i915_request_get_rcu(request);
+
+ /*
+ * What stops the following rcu_access_pointer() from occurring
+ * before the above i915_request_get_rcu()? If we were
+ * to read the value before pausing to get the reference to
+ * the request, we may not notice a change in the active
+ * tracker.
+ *
+ * The rcu_access_pointer() is a mere compiler barrier, which
+ * means both the CPU and compiler are free to perform the
+ * memory read without constraint. The compiler only has to
+ * ensure that any operations after the rcu_access_pointer()
+ * occur afterwards in program order. This means the read may
+ * be performed earlier by an out-of-order CPU, or adventurous
+ * compiler.
+ *
+ * The atomic operation at the heart of
+ * i915_request_get_rcu(), see dma_fence_get_rcu(), is
+ * atomic_inc_not_zero() which is only a full memory barrier
+ * when successful. That is, if i915_request_get_rcu()
+ * returns the request (and so with the reference counted
+ * incremented) then the following read for rcu_access_pointer()
+ * must occur after the atomic operation and so confirm
+ * that this request is the one currently being tracked.
+ *
+ * The corresponding write barrier is part of
+ * rcu_assign_pointer().
+ */
+ if (!request || request == rcu_access_pointer(active->request))
+ return rcu_pointer_handoff(request);
+
+ i915_request_put(request);
+ } while (1);
+}
+
+/**
+ * i915_active_request_get_unlocked - return a reference to the active request
+ * @active - the active tracker
+ *
+ * i915_active_request_get_unlocked() returns a reference to the active request,
+ * or NULL if the active tracker is idle. The reference is obtained under RCU,
+ * so no locking is required by the caller.
+ *
+ * The reference should be freed with i915_request_put().
+ */
+static inline struct i915_request *
+i915_active_request_get_unlocked(const struct i915_active_request *active)
+{
+ struct i915_request *request;
+
+ rcu_read_lock();
+ request = __i915_active_request_get_rcu(active);
+ rcu_read_unlock();
+
+ return request;
+}
+
+/**
+ * i915_active_request_isset - report whether the active tracker is assigned
+ * @active - the active tracker
+ *
+ * i915_active_request_isset() returns true if the active tracker is currently
+ * assigned to a request. Due to the lazy retiring, that request may be idle
+ * and this may report stale information.
+ */
+static inline bool
+i915_active_request_isset(const struct i915_active_request *active)
+{
+ return rcu_access_pointer(active->request);
+}
+
+/**
+ * i915_active_request_retire - waits until the request is retired
+ * @active - the active request on which to wait
+ *
+ * i915_active_request_retire() waits until the request is completed,
+ * and then ensures that at least the retirement handler for this
+ * @active tracker is called before returning. If the @active
+ * tracker is idle, the function returns immediately.
+ */
+static inline int __must_check
+i915_active_request_retire(struct i915_active_request *active,
+ struct mutex *mutex)
+{
+ struct i915_request *request;
+ long ret;
+
+ request = i915_active_request_raw(active, mutex);
+ if (!request)
+ return 0;
+
+ ret = i915_request_wait(request,
+ I915_WAIT_INTERRUPTIBLE | I915_WAIT_LOCKED,
+ MAX_SCHEDULE_TIMEOUT);
+ if (ret < 0)
+ return ret;
+
+ list_del_init(&active->link);
+ RCU_INIT_POINTER(active->request, NULL);
+
+ active->retire(active, request);
+
+ return 0;
+}
+
+/*
+ * GPU activity tracking
+ *
+ * Each set of commands submitted to the GPU compromises a single request that
+ * signals a fence upon completion. struct i915_request combines the
+ * command submission, scheduling and fence signaling roles. If we want to see
+ * if a particular task is complete, we need to grab the fence (struct
+ * i915_request) for that task and check or wait for it to be signaled. More
+ * often though we want to track the status of a bunch of tasks, for example
+ * to wait for the GPU to finish accessing some memory across a variety of
+ * different command pipelines from different clients. We could choose to
+ * track every single request associated with the task, but knowing that
+ * each request belongs to an ordered timeline (later requests within a
+ * timeline must wait for earlier requests), we need only track the
+ * latest request in each timeline to determine the overall status of the
+ * task.
+ *
+ * struct i915_active provides this tracking across timelines. It builds a
+ * composite shared-fence, and is updated as new work is submitted to the task,
+ * forming a snapshot of the current status. It should be embedded into the
+ * different resources that need to track their associated GPU activity to
+ * provide a callback when that GPU activity has ceased, or otherwise to
+ * provide a serialisation point either for request submission or for CPU
+ * synchronisation.
+ */
+
+void i915_active_init(struct drm_i915_private *i915,
+ struct i915_active *ref,
+ void (*retire)(struct i915_active *ref));
+
+int i915_active_ref(struct i915_active *ref,
+ u64 timeline,
+ struct i915_request *rq);
+
+int i915_active_wait(struct i915_active *ref);
+
+int i915_request_await_active(struct i915_request *rq,
+ struct i915_active *ref);
+int i915_request_await_active_request(struct i915_request *rq,
+ struct i915_active_request *active);
+
+bool i915_active_acquire(struct i915_active *ref);
+
+static inline void i915_active_cancel(struct i915_active *ref)
+{
+ GEM_BUG_ON(ref->count != 1);
+ ref->count = 0;
+}
+
+void i915_active_release(struct i915_active *ref);
+
+static inline bool
+i915_active_is_idle(const struct i915_active *ref)
+{
+ return !ref->count;
+}
+
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
+void i915_active_fini(struct i915_active *ref);
+#else
+static inline void i915_active_fini(struct i915_active *ref) { }
+#endif
+
+int i915_global_active_init(void);
+void i915_global_active_exit(void);
+
+#endif /* _I915_ACTIVE_H_ */