1/* SPDX-License-Identifier: MIT */
2/* Copyright © 2025 Intel Corporation */
3
4#ifndef __I915_WAIT_UTIL_H__
5#define __I915_WAIT_UTIL_H__
6
7#include <linux/compiler.h>
8#include <linux/delay.h>
9#include <linux/ktime.h>
10#include <linux/sched/clock.h>
11#include <linux/smp.h>
12
13/*
14 * __wait_for - magic wait macro
15 *
16 * Macro to help avoid open coding check/wait/timeout patterns. Note that it's
17 * important that we check the condition again after having timed out, since the
18 * timeout could be due to preemption or similar and we've never had a chance to
19 * check the condition before the timeout.
20 */
21#define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
22 const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
23 long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
24 int ret__; \
25 might_sleep(); \
26 for (;;) { \
27 const bool expired__ = ktime_after(ktime_get_raw(), end__); \
28 OP; \
29 /* Guarantee COND check prior to timeout */ \
30 barrier(); \
31 if (COND) { \
32 ret__ = 0; \
33 break; \
34 } \
35 if (expired__) { \
36 ret__ = -ETIMEDOUT; \
37 break; \
38 } \
39 usleep_range(wait__, wait__ * 2); \
40 if (wait__ < (Wmax)) \
41 wait__ <<= 1; \
42 } \
43 ret__; \
44})
45
46#define _wait_for(COND, US, Wmin, Wmax) __wait_for(, (COND), (US), (Wmin), \
47 (Wmax))
48#define wait_for(COND, MS) _wait_for((COND), (MS) * 1000, 10, 1000)
49
50/*
51 * If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false.
52 * On PREEMPT_RT the context isn't becoming atomic because it is used in an
53 * interrupt handler or because a spinlock_t is acquired. This leads to
54 * warnings which don't occur otherwise and therefore the check is disabled.
55 */
56#if IS_ENABLED(CONFIG_DRM_I915_DEBUG) && IS_ENABLED(CONFIG_PREEMPT_COUNT) && !defined(CONFIG_PREEMPT_RT)
57# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic())
58#else
59# define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)
60#endif
61
62#define _wait_for_atomic(COND, US, ATOMIC) \
63({ \
64 int cpu, ret, timeout = (US) * 1000; \
65 u64 base; \
66 _WAIT_FOR_ATOMIC_CHECK(ATOMIC); \
67 if (!(ATOMIC)) { \
68 preempt_disable(); \
69 cpu = smp_processor_id(); \
70 } \
71 base = local_clock(); \
72 for (;;) { \
73 u64 now = local_clock(); \
74 if (!(ATOMIC)) \
75 preempt_enable(); \
76 /* Guarantee COND check prior to timeout */ \
77 barrier(); \
78 if (COND) { \
79 ret = 0; \
80 break; \
81 } \
82 if (now - base >= timeout) { \
83 ret = -ETIMEDOUT; \
84 break; \
85 } \
86 cpu_relax(); \
87 if (!(ATOMIC)) { \
88 preempt_disable(); \
89 if (unlikely(cpu != smp_processor_id())) { \
90 timeout -= now - base; \
91 cpu = smp_processor_id(); \
92 base = local_clock(); \
93 } \
94 } \
95 } \
96 ret; \
97})
98
99#define wait_for_us(COND, US) \
100({ \
101 int ret__; \
102 BUILD_BUG_ON(!__builtin_constant_p(US)); \
103 if ((US) > 10) \
104 ret__ = _wait_for((COND), (US), 10, 10); \
105 else \
106 ret__ = _wait_for_atomic((COND), (US), 0); \
107 ret__; \
108})
109
110#define wait_for_atomic_us(COND, US) \
111({ \
112 BUILD_BUG_ON(!__builtin_constant_p(US)); \
113 BUILD_BUG_ON((US) > 50000); \
114 _wait_for_atomic((COND), (US), 1); \
115})
116
117#define wait_for_atomic(COND, MS) wait_for_atomic_us((COND), (MS) * 1000)
118
119#endif /* __I915_WAIT_UTIL_H__ */
120

source code of linux/drivers/gpu/drm/i915/i915_wait_util.h