diff options
| -rw-r--r-- | drivers/gpu/drm/drm_atomic_helper.c | 4 | ||||
| -rw-r--r-- | drivers/gpu/drm/drm_drv.c | 1 | ||||
| -rw-r--r-- | include/drm/drm_mode_config.h | 10 | ||||
| -rw-r--r-- | include/drm/drm_panic.h | 95 |
4 files changed, 110 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 39ef0a6addeb..fb97b51b38f1 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -38,6 +38,7 @@ #include <drm/drm_drv.h> #include <drm/drm_framebuffer.h> #include <drm/drm_gem_atomic_helper.h> +#include <drm/drm_panic.h> #include <drm/drm_print.h> #include <drm/drm_self_refresh_helper.h> #include <drm/drm_vblank.h> @@ -3016,6 +3017,7 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state, bool stall) { int i, ret; + unsigned long flags; struct drm_connector *connector; struct drm_connector_state *old_conn_state, *new_conn_state; struct drm_crtc *crtc; @@ -3099,6 +3101,7 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state, } } + drm_panic_lock(state->dev, flags); for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) { WARN_ON(plane->state != old_plane_state); @@ -3108,6 +3111,7 @@ int drm_atomic_helper_swap_state(struct drm_atomic_state *state, state->planes[i].state = old_plane_state; plane->state = new_plane_state; } + drm_panic_unlock(state->dev, flags); for_each_oldnew_private_obj_in_state(state, obj, old_obj_state, new_obj_state, i) { WARN_ON(obj->state != old_obj_state); diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index 243cacb3575c..c157500b3135 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -638,6 +638,7 @@ static int drm_dev_init(struct drm_device *dev, mutex_init(&dev->filelist_mutex); mutex_init(&dev->clientlist_mutex); mutex_init(&dev->master_mutex); + raw_spin_lock_init(&dev->mode_config.panic_lock); ret = drmm_add_action_or_reset(dev, drm_dev_init_release, NULL); if (ret) diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h index 9d8acf7a10eb..06d7777a881f 100644 --- a/include/drm/drm_mode_config.h +++ b/include/drm/drm_mode_config.h @@ -506,6 +506,16 @@ struct drm_mode_config { struct list_head plane_list; /** + * @panic_lock: + * + * Raw spinlock used to protect critical sections of code that access + * the display hardware or modeset software state, which the panic + * printing code must be protected against. See drm_panic_trylock(), + * drm_panic_lock() and drm_panic_unlock(). + */ + struct raw_spinlock panic_lock; + + /** * @num_crtc: * * Number of CRTCs on this device linked with &drm_crtc.head. This is invariant over the lifetime diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h new file mode 100644 index 000000000000..967e02ccc6d5 --- /dev/null +++ b/include/drm/drm_panic.h @@ -0,0 +1,95 @@ +/* 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__ */ |