@@ -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,
}
}
+ flags = drm_panic_lock(state->dev);
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);
@@ -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)
@@ -505,6 +505,16 @@ 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:
*
new file mode 100644
@@ -0,0 +1,107 @@
+/* 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: 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().
+ *
+ * Returns:
+ *
+ * 0 when failing to acquire the raw spinlock, nonzero on success.
+ */
+static inline int drm_panic_trylock(struct drm_device *dev, unsigned long *flags)
+{
+ return raw_spin_trylock_irqsave(&dev->mode_config.panic_lock, *flags);
+}
+
+/**
+ * drm_panic_lock - protect panic printing relevant state
+ * @dev: struct drm_device
+ *
+ * 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.
+ *
+ * Returns:
+ *
+ * The irqflags needed to call drm_panic_unlock().
+ */
+static inline unsigned long drm_panic_lock(struct drm_device *dev)
+{
+ unsigned long flags;
+
+ raw_spin_lock_irqsave(&dev->mode_config.panic_lock, flags);
+ return 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().
+ */
+static inline void drm_panic_unlock(struct drm_device *dev, unsigned long flags)
+{
+ raw_spin_unlock_irqrestore(&dev->mode_config.panic_lock, flags);
+}
+
+#endif /* __DRM_PANIC_H__ */