tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/* SPDX-License-Identifier: GPL-2.0 or MIT */
2
3/*
4 * Copyright (c) 2024 Intel
5 * Copyright (c) 2024 Red Hat
6 */
7
8#ifndef __DRM_PANIC_H__
9#define __DRM_PANIC_H__
10
11#include <linux/module.h>
12#include <linux/types.h>
13#include <linux/iosys-map.h>
14
15#include <drm/drm_device.h>
16#include <drm/drm_fourcc.h>
17
18/**
19 * struct drm_scanout_buffer - DRM scanout buffer
20 *
21 * This structure holds the information necessary for drm_panic to draw the
22 * panic screen, and display it.
23 */
24struct drm_scanout_buffer {
25 /**
26 * @format:
27 *
28 * drm format of the scanout buffer.
29 */
30 const struct drm_format_info *format;
31
32 /**
33 * @map:
34 *
35 * Virtual address of the scanout buffer, either in memory or iomem.
36 * The scanout buffer should be in linear format, and can be directly
37 * sent to the display hardware. Tearing is not an issue for the panic
38 * screen.
39 */
40 struct iosys_map map[DRM_FORMAT_MAX_PLANES];
41
42 /**
43 * @width: Width of the scanout buffer, in pixels.
44 */
45 unsigned int width;
46
47 /**
48 * @height: Height of the scanout buffer, in pixels.
49 */
50 unsigned int height;
51
52 /**
53 * @pitch: Length in bytes between the start of two consecutive lines.
54 */
55 unsigned int pitch[DRM_FORMAT_MAX_PLANES];
56
57 /**
58 * @set_pixel: Optional function, to set a pixel color on the
59 * framebuffer. It allows to handle special tiling format inside the
60 * driver.
61 */
62 void (*set_pixel)(struct drm_scanout_buffer *sb, unsigned int x,
63 unsigned int y, u32 color);
64
65};
66
67/**
68 * drm_panic_trylock - try to enter the panic printing critical section
69 * @dev: struct drm_device
70 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
71 *
72 * This function must be called by any panic printing code. The panic printing
73 * attempt must be aborted if the trylock fails.
74 *
75 * Panic printing code can make the following assumptions while holding the
76 * panic lock:
77 *
78 * - Anything protected by drm_panic_lock() and drm_panic_unlock() pairs is safe
79 * to access.
80 *
81 * - Furthermore the panic printing code only registers in drm_dev_unregister()
82 * and gets removed in drm_dev_unregister(). This allows the panic code to
83 * safely access any state which is invariant in between these two function
84 * calls, like the list of planes &drm_mode_config.plane_list or most of the
85 * struct drm_plane structure.
86 *
87 * Specifically thanks to the protection around plane updates in
88 * drm_atomic_helper_swap_state() the following additional guarantees hold:
89 *
90 * - It is safe to deference the drm_plane.state pointer.
91 *
92 * - Anything in struct drm_plane_state or the driver's subclass thereof which
93 * stays invariant after the atomic check code has finished is safe to access.
94 * Specifically this includes the reference counted pointers to framebuffer
95 * and buffer objects.
96 *
97 * - Anything set up by &drm_plane_helper_funcs.fb_prepare and cleaned up
98 * &drm_plane_helper_funcs.fb_cleanup is safe to access, as long as it stays
99 * invariant between these two calls. This also means that for drivers using
100 * dynamic buffer management the framebuffer is pinned, and therefer all
101 * relevant datastructures can be accessed without taking any further locks
102 * (which would be impossible in panic context anyway).
103 *
104 * - Importantly, software and hardware state set up by
105 * &drm_plane_helper_funcs.begin_fb_access and
106 * &drm_plane_helper_funcs.end_fb_access is not safe to access.
107 *
108 * Drivers must not make any assumptions about the actual state of the hardware,
109 * unless they explicitly protected these hardware access with drm_panic_lock()
110 * and drm_panic_unlock().
111 *
112 * Return:
113 * %0 when failing to acquire the raw spinlock, nonzero on success.
114 */
115#define drm_panic_trylock(dev, flags) \
116 raw_spin_trylock_irqsave(&(dev)->mode_config.panic_lock, flags)
117
118/**
119 * drm_panic_lock - protect panic printing relevant state
120 * @dev: struct drm_device
121 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
122 *
123 * This function must be called to protect software and hardware state that the
124 * panic printing code must be able to rely on. The protected sections must be
125 * as small as possible. It uses the irqsave/irqrestore variant, and can be
126 * called from irq handler. Examples include:
127 *
128 * - Access to peek/poke or other similar registers, if that is the way the
129 * driver prints the pixels into the scanout buffer at panic time.
130 *
131 * - Updates to pointers like &drm_plane.state, allowing the panic handler to
132 * safely deference these. This is done in drm_atomic_helper_swap_state().
133 *
134 * - An state that isn't invariant and that the driver must be able to access
135 * during panic printing.
136 */
137
138#define drm_panic_lock(dev, flags) \
139 raw_spin_lock_irqsave(&(dev)->mode_config.panic_lock, flags)
140
141/**
142 * drm_panic_unlock - end of the panic printing critical section
143 * @dev: struct drm_device
144 * @flags: irq flags that were returned when acquiring the lock
145 *
146 * Unlocks the raw spinlock acquired by either drm_panic_lock() or
147 * drm_panic_trylock().
148 */
149#define drm_panic_unlock(dev, flags) \
150 raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
151
152#endif /* __DRM_PANIC_H__ */