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/* SPDX-License-Identifier: GPL-2.0 or MIT */
#ifndef __DRM_PANIC_H__
#define __DRM_PANIC_H__
#include <drm/drm_device.h>
/*
* Copyright (c) 2024 Intel
*/
/**
* drm_panic_trylock - try to enter the panic printing critical section
* @dev: struct drm_device
* @flags: unsigned long irq flags you need to pass to the unlock() counterpart
*
* This function must be called by any panic printing code. The panic printing
* attempt must be aborted if the trylock fails.
*
* Panic printing code can make the following assumptions while holding the
* panic lock:
*
* - Anything protected by drm_panic_lock() and drm_panic_unlock() pairs is safe
* to access.
*
* - Furthermore the panic printing code only registers in drm_dev_unregister()
* and gets removed in drm_dev_unregister(). This allows the panic code to
* safely access any state which is invariant in between these two function
* calls, like the list of planes &drm_mode_config.plane_list or most of the
* struct drm_plane structure.
*
* Specifically thanks to the protection around plane updates in
* drm_atomic_helper_swap_state() the following additional guarantees hold:
*
* - It is safe to deference the drm_plane.state pointer.
*
* - Anything in struct drm_plane_state or the driver's subclass thereof which
* stays invariant after the atomic check code has finished is safe to access.
* Specifically this includes the reference counted pointers to framebuffer
* and buffer objects.
*
* - Anything set up by &drm_plane_helper_funcs.fb_prepare and cleaned up
* &drm_plane_helper_funcs.fb_cleanup is safe to access, as long as it stays
* invariant between these two calls. This also means that for drivers using
* dynamic buffer management the framebuffer is pinned, and therefer all
* relevant datastructures can be accessed without taking any further locks
* (which would be impossible in panic context anyway).
*
* - Importantly, software and hardware state set up by
* &drm_plane_helper_funcs.begin_fb_access and
* &drm_plane_helper_funcs.end_fb_access is not safe to access.
*
* Drivers must not make any assumptions about the actual state of the hardware,
* unless they explicitly protected these hardware access with drm_panic_lock()
* and drm_panic_unlock().
*
* Return:
* %0 when failing to acquire the raw spinlock, nonzero on success.
*/
#define drm_panic_trylock(dev, flags) \
raw_spin_trylock_irqsave(&(dev)->mode_config.panic_lock, flags)
/**
* drm_panic_lock - protect panic printing relevant state
* @dev: struct drm_device
* @flags: unsigned long irq flags you need to pass to the unlock() counterpart
*
* This function must be called to protect software and hardware state that the
* panic printing code must be able to rely on. The protected sections must be
* as small as possible. It uses the irqsave/irqrestore variant, and can be
* called from irq handler. Examples include:
*
* - Access to peek/poke or other similar registers, if that is the way the
* driver prints the pixels into the scanout buffer at panic time.
*
* - Updates to pointers like &drm_plane.state, allowing the panic handler to
* safely deference these. This is done in drm_atomic_helper_swap_state().
*
* - An state that isn't invariant and that the driver must be able to access
* during panic printing.
*/
#define drm_panic_lock(dev, flags) \
raw_spin_lock_irqsave(&(dev)->mode_config.panic_lock, flags)
/**
* drm_panic_unlock - end of the panic printing critical section
* @dev: struct drm_device
* @flags: irq flags that were returned when acquiring the lock
*
* Unlocks the raw spinlock acquired by either drm_panic_lock() or
* drm_panic_trylock().
*/
#define drm_panic_unlock(dev, flags) \
raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
#endif /* __DRM_PANIC_H__ */
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