1/* SPDX-License-Identifier: GPL-2.0 or MIT */
2#ifndef __DRM_PANIC_H__
3#define __DRM_PANIC_H__
4
5#include <linux/module.h>
6#include <linux/types.h>
7#include <linux/iosys-map.h>
8
9#include <drm/drm_device.h>
10#include <drm/drm_fourcc.h>
11/*
12 * Copyright (c) 2024 Intel
13 */
14
15/**
16 * struct drm_scanout_buffer - DRM scanout buffer
17 *
18 * This structure holds the information necessary for drm_panic to draw the
19 * panic screen, and display it.
20 */
21struct drm_scanout_buffer {
22	/**
23	 * @format:
24	 *
25	 * drm format of the scanout buffer.
26	 */
27	const struct drm_format_info *format;
28
29	/**
30	 * @map:
31	 *
32	 * Virtual address of the scanout buffer, either in memory or iomem.
33	 * The scanout buffer should be in linear format, and can be directly
34	 * sent to the display hardware. Tearing is not an issue for the panic
35	 * screen.
36	 */
37	struct iosys_map map[DRM_FORMAT_MAX_PLANES];
38
39	/**
40	 * @width: Width of the scanout buffer, in pixels.
41	 */
42	unsigned int width;
43
44	/**
45	 * @height: Height of the scanout buffer, in pixels.
46	 */
47	unsigned int height;
48
49	/**
50	 * @pitch: Length in bytes between the start of two consecutive lines.
51	 */
52	unsigned int pitch[DRM_FORMAT_MAX_PLANES];
53};
54
55/**
56 * drm_panic_trylock - try to enter the panic printing critical section
57 * @dev: struct drm_device
58 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
59 *
60 * This function must be called by any panic printing code. The panic printing
61 * attempt must be aborted if the trylock fails.
62 *
63 * Panic printing code can make the following assumptions while holding the
64 * panic lock:
65 *
66 * - Anything protected by drm_panic_lock() and drm_panic_unlock() pairs is safe
67 *   to access.
68 *
69 * - Furthermore the panic printing code only registers in drm_dev_unregister()
70 *   and gets removed in drm_dev_unregister(). This allows the panic code to
71 *   safely access any state which is invariant in between these two function
72 *   calls, like the list of planes &drm_mode_config.plane_list or most of the
73 *   struct drm_plane structure.
74 *
75 * Specifically thanks to the protection around plane updates in
76 * drm_atomic_helper_swap_state() the following additional guarantees hold:
77 *
78 * - It is safe to deference the drm_plane.state pointer.
79 *
80 * - Anything in struct drm_plane_state or the driver's subclass thereof which
81 *   stays invariant after the atomic check code has finished is safe to access.
82 *   Specifically this includes the reference counted pointers to framebuffer
83 *   and buffer objects.
84 *
85 * - Anything set up by &drm_plane_helper_funcs.fb_prepare and cleaned up
86 *   &drm_plane_helper_funcs.fb_cleanup is safe to access, as long as it stays
87 *   invariant between these two calls. This also means that for drivers using
88 *   dynamic buffer management the framebuffer is pinned, and therefer all
89 *   relevant datastructures can be accessed without taking any further locks
90 *   (which would be impossible in panic context anyway).
91 *
92 * - Importantly, software and hardware state set up by
93 *   &drm_plane_helper_funcs.begin_fb_access and
94 *   &drm_plane_helper_funcs.end_fb_access is not safe to access.
95 *
96 * Drivers must not make any assumptions about the actual state of the hardware,
97 * unless they explicitly protected these hardware access with drm_panic_lock()
98 * and drm_panic_unlock().
99 *
100 * Return:
101 * %0 when failing to acquire the raw spinlock, nonzero on success.
102 */
103#define drm_panic_trylock(dev, flags) \
104	raw_spin_trylock_irqsave(&(dev)->mode_config.panic_lock, flags)
105
106/**
107 * drm_panic_lock - protect panic printing relevant state
108 * @dev: struct drm_device
109 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
110 *
111 * This function must be called to protect software and hardware state that the
112 * panic printing code must be able to rely on. The protected sections must be
113 * as small as possible. It uses the irqsave/irqrestore variant, and can be
114 * called from irq handler. Examples include:
115 *
116 * - Access to peek/poke or other similar registers, if that is the way the
117 *   driver prints the pixels into the scanout buffer at panic time.
118 *
119 * - Updates to pointers like &drm_plane.state, allowing the panic handler to
120 *   safely deference these. This is done in drm_atomic_helper_swap_state().
121 *
122 * - An state that isn't invariant and that the driver must be able to access
123 *   during panic printing.
124 */
125
126#define drm_panic_lock(dev, flags) \
127	raw_spin_lock_irqsave(&(dev)->mode_config.panic_lock, flags)
128
129/**
130 * drm_panic_unlock - end of the panic printing critical section
131 * @dev: struct drm_device
132 * @flags: irq flags that were returned when acquiring the lock
133 *
134 * Unlocks the raw spinlock acquired by either drm_panic_lock() or
135 * drm_panic_trylock().
136 */
137#define drm_panic_unlock(dev, flags) \
138	raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
139
140#ifdef CONFIG_DRM_PANIC
141
142void drm_panic_register(struct drm_device *dev);
143void drm_panic_unregister(struct drm_device *dev);
144
145#else
146
147static inline void drm_panic_register(struct drm_device *dev) {}
148static inline void drm_panic_unregister(struct drm_device *dev) {}
149
150#endif
151
152#endif /* __DRM_PANIC_H__ */
153