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