1  /* SPDX-License-Identifier: MIT */
2  /*
3   * Copyright © 2019 Intel Corporation
4   */
5  
6  #ifndef __INTEL_BREADCRUMBS_TYPES__
7  #define __INTEL_BREADCRUMBS_TYPES__
8  
9  #include <linux/irq_work.h>
10  #include <linux/kref.h>
11  #include <linux/list.h>
12  #include <linux/spinlock.h>
13  #include <linux/types.h>
14  
15  #include "intel_engine_types.h"
16  #include "intel_wakeref.h"
17  
18  /*
19   * Rather than have every client wait upon all user interrupts,
20   * with the herd waking after every interrupt and each doing the
21   * heavyweight seqno dance, we delegate the task (of being the
22   * bottom-half of the user interrupt) to the first client. After
23   * every interrupt, we wake up one client, who does the heavyweight
24   * coherent seqno read and either goes back to sleep (if incomplete),
25   * or wakes up all the completed clients in parallel, before then
26   * transferring the bottom-half status to the next client in the queue.
27   *
28   * Compared to walking the entire list of waiters in a single dedicated
29   * bottom-half, we reduce the latency of the first waiter by avoiding
30   * a context switch, but incur additional coherent seqno reads when
31   * following the chain of request breadcrumbs. Since it is most likely
32   * that we have a single client waiting on each seqno, then reducing
33   * the overhead of waking that client is much preferred.
34   */
35  struct intel_breadcrumbs {
36  	struct kref ref;
37  	atomic_t active;
38  
39  	spinlock_t signalers_lock; /* protects the list of signalers */
40  	struct list_head signalers;
41  	struct llist_head signaled_requests;
42  	atomic_t signaler_active;
43  
44  	spinlock_t irq_lock; /* protects the interrupt from hardirq context */
45  	struct irq_work irq_work; /* for use from inside irq_lock */
46  	unsigned int irq_enabled;
47  	intel_wakeref_t irq_armed;
48  
49  	/* Not all breadcrumbs are attached to physical HW */
50  	intel_engine_mask_t	engine_mask;
51  	struct intel_engine_cs *irq_engine;
52  	bool	(*irq_enable)(struct intel_breadcrumbs *b);
53  	void	(*irq_disable)(struct intel_breadcrumbs *b);
54  };
55  
56  #endif /* __INTEL_BREADCRUMBS_TYPES__ */
57