xref: /linux/include/drm/drm_panic.h (revision f4db95b68ae68ebaf91d35cc0487ac1cbd04261e)
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  */
24 struct 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__ */
153