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#ifdef CONFIG_DRM_PANIC
 68
 69/**
 70 * drm_panic_trylock - try to enter the panic printing critical section
 71 * @dev: struct drm_device
 72 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
 73 *
 74 * This function must be called by any panic printing code. The panic printing
 75 * attempt must be aborted if the trylock fails.
 76 *
 77 * Panic printing code can make the following assumptions while holding the
 78 * panic lock:
 79 *
 80 * - Anything protected by drm_panic_lock() and drm_panic_unlock() pairs is safe
 81 *   to access.
 82 *
 83 * - Furthermore the panic printing code only registers in drm_dev_unregister()
 84 *   and gets removed in drm_dev_unregister(). This allows the panic code to
 85 *   safely access any state which is invariant in between these two function
 86 *   calls, like the list of planes &drm_mode_config.plane_list or most of the
 87 *   struct drm_plane structure.
 88 *
 89 * Specifically thanks to the protection around plane updates in
 90 * drm_atomic_helper_swap_state() the following additional guarantees hold:
 91 *
 92 * - It is safe to deference the drm_plane.state pointer.
 93 *
 94 * - Anything in struct drm_plane_state or the driver's subclass thereof which
 95 *   stays invariant after the atomic check code has finished is safe to access.
 96 *   Specifically this includes the reference counted pointers to framebuffer
 97 *   and buffer objects.
 98 *
 99 * - Anything set up by &drm_plane_helper_funcs.fb_prepare and cleaned up
100 *   &drm_plane_helper_funcs.fb_cleanup is safe to access, as long as it stays
101 *   invariant between these two calls. This also means that for drivers using
102 *   dynamic buffer management the framebuffer is pinned, and therefer all
103 *   relevant datastructures can be accessed without taking any further locks
104 *   (which would be impossible in panic context anyway).
105 *
106 * - Importantly, software and hardware state set up by
107 *   &drm_plane_helper_funcs.begin_fb_access and
108 *   &drm_plane_helper_funcs.end_fb_access is not safe to access.
109 *
110 * Drivers must not make any assumptions about the actual state of the hardware,
111 * unless they explicitly protected these hardware access with drm_panic_lock()
112 * and drm_panic_unlock().
113 *
114 * Return:
115 * %0 when failing to acquire the raw spinlock, nonzero on success.
116 */
117#define drm_panic_trylock(dev, flags) \
118	raw_spin_trylock_irqsave(&(dev)->mode_config.panic_lock, flags)
119
120/**
121 * drm_panic_lock - protect panic printing relevant state
122 * @dev: struct drm_device
123 * @flags: unsigned long irq flags you need to pass to the unlock() counterpart
124 *
125 * This function must be called to protect software and hardware state that the
126 * panic printing code must be able to rely on. The protected sections must be
127 * as small as possible. It uses the irqsave/irqrestore variant, and can be
128 * called from irq handler. Examples include:
129 *
130 * - Access to peek/poke or other similar registers, if that is the way the
131 *   driver prints the pixels into the scanout buffer at panic time.
132 *
133 * - Updates to pointers like &drm_plane.state, allowing the panic handler to
134 *   safely deference these. This is done in drm_atomic_helper_swap_state().
135 *
136 * - An state that isn't invariant and that the driver must be able to access
137 *   during panic printing.
138 */
139
140#define drm_panic_lock(dev, flags) \
141	raw_spin_lock_irqsave(&(dev)->mode_config.panic_lock, flags)
142
143/**
144 * drm_panic_unlock - end of the panic printing critical section
145 * @dev: struct drm_device
146 * @flags: irq flags that were returned when acquiring the lock
147 *
148 * Unlocks the raw spinlock acquired by either drm_panic_lock() or
149 * drm_panic_trylock().
150 */
151#define drm_panic_unlock(dev, flags) \
152	raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
153
154#else
155
156static inline bool drm_panic_trylock(struct drm_device *dev, unsigned long flags)
157{
158	return true;
159}
160
161static inline void drm_panic_lock(struct drm_device *dev, unsigned long flags) {}
162static inline void drm_panic_unlock(struct drm_device *dev, unsigned long flags) {}
163
164#endif
165
166#endif /* __DRM_PANIC_H__ */