drm/panic: Add a drm panic handler

This module displays a user friendly message when a kernel panic
occurs. It currently doesn't contain any debug information,
but that can be added later.

v2
 * Use get_scanout_buffer() instead of the drm client API.
  (Thomas Zimmermann)
 * Add the panic reason to the panic message (Nerdopolis)
 * Add an exclamation mark (Nerdopolis)

v3
 * Rework the drawing functions, to write the pixels line by line and
 to use the drm conversion helper to support other formats.
 (Thomas Zimmermann)

v4
 * Use drm_fb_r1_to_32bit for fonts (Thomas Zimmermann)
 * Remove the default y to DRM_PANIC config option (Thomas Zimmermann)
 * Add foreground/background color config option
 * Fix the bottom lines not painted if the framebuffer height
   is not a multiple of the font height.
 * Automatically register the device to drm_panic, if the function
   get_scanout_buffer exists. (Thomas Zimmermann)

v5
 * Change the drawing API, use drm_fb_blit_from_r1() to draw the font.
 * Also add drm_fb_fill() to fill area with background color.
 * Add draw_pixel_xy() API for drivers that can't provide a linear buffer.
 * Add a flush() callback for drivers that needs to synchronize the buffer.
 * Add a void *private field, so drivers can pass private data to
   draw_pixel_xy() and flush().

v6
 * Fix sparse warning for panic_msg and logo.

v7
 * Add select DRM_KMS_HELPER for the color conversion functions.

v8
 * Register directly each plane to the panic notifier (Sima)
 * Add raw_spinlock to properly handle concurrency (Sima)
 * Register plane instead of device, to avoid looping through plane
   list, and simplify code.
 * Replace get_scanout_buffer() logic with drm_panic_set_buffer()
  (Thomas Zimmermann)
 * Removed the draw_pixel_xy() API, will see later if it can be added back.

v9
 * Revert to using get_scanout_buffer() (Sima)
 * Move get_scanout_buffer() and panic_flush() to the plane helper
   functions (Thomas Zimmermann)
 * Register all planes with get_scanout_buffer() to the panic notifier
 * Use drm_panic_lock() to protect against race (Sima)

v10
 * Move blit and fill functions back in drm_panic (Thomas Zimmermann).
 * Simplify the text drawing functions.
 * Use kmsg_dumper instead of panic_notifier (Sima).

v12
 * Use array for map and pitch in struct drm_scanout_buffer
   to support multi-planar format later. (Thomas Zimmermann)
 * Better indent struct drm_scanout_buffer declaration. (Thomas Zimmermann)

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240409163432.352518-3-jfalempe@redhat.com
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

3 files changed, 102 insertions, 0 deletions

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 9ed42469540e..ec59015aec3c 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -48,6 +48,7 @@
  * To make this clear all the helper vtables are pulled together in this location here.
  */
 
+struct drm_scanout_buffer;
 struct drm_writeback_connector;
 struct drm_writeback_job;
 
@@ -1443,6 +1444,44 @@ struct drm_plane_helper_funcs {
 	 */
 	void (*atomic_async_update)(struct drm_plane *plane,
 				    struct drm_atomic_state *state);
+
+	/**
+	 * @get_scanout_buffer:
+	 *
+	 * Get the current scanout buffer, to display a message with drm_panic.
+	 * The driver should do the minimum changes to provide a buffer,
+	 * that can be used to display the panic screen. Currently only linear
+	 * buffers are supported. Non-linear buffer support is on the TODO list.
+	 * The device &dev.mode_config.panic_lock is taken before calling this
+	 * function, so you can safely access the &plane.state
+	 * It is called from a panic callback, and must follow its restrictions.
+	 * Please look the documentation at drm_panic_trylock() for an in-depth
+	 * discussions of what's safe and what is not allowed.
+	 * It's a best effort mode, so it's expected that in some complex cases
+	 * the panic screen won't be displayed.
+	 * The returned &drm_scanout_buffer.map must be valid if no error code is
+	 * returned.
+	 *
+	 * Return:
+	 * %0 on success, negative errno on failure.
+	 */
+	int (*get_scanout_buffer)(struct drm_plane *plane,
+				  struct drm_scanout_buffer *sb);
+
+	/**
+	 * @panic_flush:
+	 *
+	 * It is used by drm_panic, and is called after the panic screen is
+	 * drawn to the scanout buffer. In this function, the driver
+	 * can send additional commands to the hardware, to make the scanout
+	 * buffer visible.
+	 * It is only called if get_scanout_buffer() returned successfully, and
+	 * the &dev.mode_config.panic_lock is held during the entire sequence.
+	 * It is called from a panic callback, and must follow its restrictions.
+	 * Please look the documentation at drm_panic_trylock() for an in-depth
+	 * discussions of what's safe and what is not allowed.
+	 */
+	void (*panic_flush)(struct drm_plane *plane);
 };
 
 /**
diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h
index 967e02ccc6d5..822dbb1aa9d6 100644
--- a/include/drm/drm_panic.h
+++ b/include/drm/drm_panic.h
@@ -2,12 +2,57 @@
 #ifndef __DRM_PANIC_H__
 #define __DRM_PANIC_H__
 
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/iosys-map.h>
+
 #include <drm/drm_device.h>
+#include <drm/drm_fourcc.h>
 /*
  * Copyright (c) 2024 Intel
  */
 
 /**
+ * struct drm_scanout_buffer - DRM scanout buffer
+ *
+ * This structure holds the information necessary for drm_panic to draw the
+ * panic screen, and display it.
+ */
+struct drm_scanout_buffer {
+	/**
+	 * @format:
+	 *
+	 * drm format of the scanout buffer.
+	 */
+	const struct drm_format_info *format;
+
+	/**
+	 * @map:
+	 *
+	 * Virtual address of the scanout buffer, either in memory or iomem.
+	 * The scanout buffer should be in linear format, and can be directly
+	 * sent to the display hardware. Tearing is not an issue for the panic
+	 * screen.
+	 */
+	struct iosys_map map[DRM_FORMAT_MAX_PLANES];
+
+	/**
+	 * @width: Width of the scanout buffer, in pixels.
+	 */
+	unsigned int width;
+
+	/**
+	 * @height: Height of the scanout buffer, in pixels.
+	 */
+	unsigned int height;
+
+	/**
+	 * @pitch: Length in bytes between the start of two consecutive lines.
+	 */
+	unsigned int pitch[DRM_FORMAT_MAX_PLANES];
+};
+
+/**
  * 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
@@ -92,4 +137,16 @@
 #define drm_panic_unlock(dev, flags) \
 	raw_spin_unlock_irqrestore(&(dev)->mode_config.panic_lock, flags)
 
+#ifdef CONFIG_DRM_PANIC
+
+void drm_panic_register(struct drm_device *dev);
+void drm_panic_unregister(struct drm_device *dev);
+
+#else
+
+static inline void drm_panic_register(struct drm_device *dev) {}
+static inline void drm_panic_unregister(struct drm_device *dev) {}
+
+#endif
+
 #endif /* __DRM_PANIC_H__ */
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index ec1112208b73..9507542121fa 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -25,6 +25,7 @@
 
 #include <linux/list.h>
 #include <linux/ctype.h>
+#include <linux/kmsg_dump.h>
 #include <drm/drm_mode_object.h>
 #include <drm/drm_color_mgmt.h>
 #include <drm/drm_rect.h>
@@ -780,6 +781,11 @@ struct drm_plane {
 	 * @hotspot_y_property: property to set mouse hotspot y offset.
 	 */
 	struct drm_property *hotspot_y_property;
+
+	/**
+	 * @kmsg_panic: Used to register a panic notifier for this plane
+	 */
+	struct kmsg_dumper kmsg_panic;
 };
 
 #define obj_to_plane(x) container_of(x, struct drm_plane, base)