[PATCH v3 2/3] drm/panic: Add a drm panic handler

[Jocelyn Falempe <jfalempe@redhat.com>]

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)

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
---
 drivers/gpu/drm/Kconfig     |  11 ++
 drivers/gpu/drm/Makefile    |   1 +
 drivers/gpu/drm/drm_drv.c   |   3 +
 drivers/gpu/drm/drm_panic.c | 366 ++++++++++++++++++++++++++++++++++++
 include/drm/drm_drv.h       |  14 ++
 include/drm/drm_panic.h     |  41 ++++
 6 files changed, 436 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index afb3b2f5f425..98d78f865180 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -99,6 +99,17 @@ config DRM_KMS_HELPER
 	help
 	  CRTC helpers for KMS drivers.
 
+config DRM_PANIC
+	bool "Display a user-friendly message when a kernel panic occurs"
+	depends on DRM && !FRAMEBUFFER_CONSOLE
+	select FONT_SUPPORT
+	default y if DRM_SIMPLEDRM
+	help
+	  Enable a drm panic handler, which will display a user-friendly message
+	  when a kernel panic occurs. It's useful when using a user-space
+	  console instead of fbcon.
+	  It will only work if your graphic driver supports this feature.
+
 config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
         bool "Enable refcount backtrace history in the DP MST helpers"
 	depends on STACKTRACE_SUPPORT
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 7a09a89b493b..a525dd9a2751 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -72,6 +72,7 @@ drm-$(CONFIG_DRM_PRIVACY_SCREEN) += \
 	drm_privacy_screen_x86.o
 drm-$(CONFIG_DRM_ACCEL) += ../../accel/drm_accel.o
 obj-$(CONFIG_DRM)	+= drm.o
+drm-$(CONFIG_DRM_PANIC) += drm_panic.o
 
 obj-$(CONFIG_DRM_PANEL_ORIENTATION_QUIRKS) += drm_panel_orientation_quirks.o
 
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 12687dd9e1ac..0e0f1e258845 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -45,6 +45,7 @@
 #include <drm/drm_mode_object.h>
 #include <drm/drm_print.h>
 #include <drm/drm_privacy_screen_machine.h>
+#include <drm/drm_panic.h>
 
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"
@@ -1067,6 +1068,7 @@ static void drm_core_exit(void)
 	unregister_chrdev(DRM_MAJOR, "drm");
 	debugfs_remove(drm_debugfs_root);
 	drm_sysfs_destroy();
+	drm_panic_exit();
 	idr_destroy(&drm_minors_idr);
 	drm_connector_ida_destroy();
 }
@@ -1078,6 +1080,7 @@ static int __init drm_core_init(void)
 	drm_connector_ida_init();
 	idr_init(&drm_minors_idr);
 	drm_memcpy_init_early();
+	drm_panic_init();
 
 	ret = drm_sysfs_init();
 	if (ret < 0) {
diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
new file mode 100644
index 000000000000..1d93e4dbed9a
--- /dev/null
+++ b/drivers/gpu/drm/drm_panic.c
@@ -0,0 +1,366 @@
+// SPDX-License-Identifier: GPL-2.0 or MIT
+/*
+ * Copyright (c) 2023 Jocelyn Falempe <jfalempe@redhat.com>
+ * inspired by the drm_log driver from David Herrmann <dh.herrmann@gmail.com>
+ * Tux Ascii art taken from cowsay written by Tony Monroe
+ */
+
+#include <linux/font.h>
+#include <linux/iosys-map.h>
+#include <linux/kdebug.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/panic_notifier.h>
+#include <linux/types.h>
+
+#include <drm/drm_drv.h>
+#include <drm/drm_format_helper.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_panic.h>
+#include <drm/drm_print.h>
+
+
+MODULE_AUTHOR("Jocelyn Falempe");
+MODULE_DESCRIPTION("DRM PANIC");
+MODULE_LICENSE("GPL");
+
+/**
+ * DOC: DRM Panic
+ *
+ * This module displays a user friendly message on screen when a kernel panic
+ * occurs. It's useful when using a user-space console instead of fbcon.
+ * It's intended for end-user, so have minimal technical/debug information.
+ *
+ * It will display only one static frame, so performance optimizations are low
+ * priority as the machine is already in an unusable state.
+ */
+
+/*
+ * List of active drm devices that can render a panic
+ */
+struct dpanic_drm_device {
+	struct list_head head;
+	struct drm_device *dev;
+};
+
+struct dpanic_line {
+	u32 len;
+	const char *txt;
+};
+
+#define PANIC_LINE(s) {.len = sizeof(s) - 1, .txt = s}
+
+struct dpanic_line panic_msg[] = {
+	PANIC_LINE("KERNEL PANIC !"),
+	PANIC_LINE(""),
+	PANIC_LINE("Please reboot your computer."),
+	PANIC_LINE(""),
+	PANIC_LINE(""), /* overwritten with panic reason */
+};
+
+const struct dpanic_line logo[] = {
+	PANIC_LINE("     .--.        _"),
+	PANIC_LINE("    |o_o |      | |"),
+	PANIC_LINE("    |:_/ |      | |"),
+	PANIC_LINE("   //   \\ \\     |_|"),
+	PANIC_LINE("  (|     | )     _"),
+	PANIC_LINE(" /'\\_   _/`\\    (_)"),
+	PANIC_LINE(" \\___)=(___/"),
+};
+
+static LIST_HEAD(dpanic_devices);
+static DEFINE_MUTEX(dpanic_lock);
+
+/*
+ * This buffer is used to convert xrgb8888 to the scanout buffer format.
+ * It is allocated when the first client register, and freed when the last client
+ * unregisters.
+ * There is no need for mutex, as the panic garantee that only 1 CPU is still
+ * running, and preemption is disabled.
+ */
+#define DRM_PANIC_MAX_WIDTH 8096
+static u32 *dpanic_line_buf;
+static u32 fg_color = le32_to_cpu(0x00ffffff);
+static u32 bg_color = le32_to_cpu(0x00000000);
+
+static void dpanic_draw_line(const struct dpanic_line *msg, size_t left_margin,
+			     size_t l, size_t width, const struct font_desc *font)
+{
+	size_t x, i, j;
+	const u8 *src;
+	size_t src_stride = DIV_ROUND_UP(font->width, 8);
+	u32 *dst = dpanic_line_buf;
+
+	for (x = 0; x < left_margin * font->width; x++)
+		*dst++ = bg_color;
+
+	for (i = 0; i < msg->len; i++) {
+		for (j = 0; j < font->width; j++) {
+			src = font->data + (msg->txt[i] * font->height + l) * src_stride;
+			*dst++ = (src[j / 8] & (0x80 >> (j % 8))) ? fg_color : bg_color;
+		}
+	}
+	for (x = (left_margin + msg->len) * font->width; x < width ; x++)
+		*dst++ = bg_color;
+}
+
+static void dpanic_draw_txt_line(const struct dpanic_line *msg, size_t left_margin, size_t y,
+			  struct drm_scanout_buffer *sb,
+			  const struct font_desc *font,
+			  void (*convert)(void *dbuf, const void *sbuf, unsigned int npixels))
+{
+	size_t dst_off;
+	size_t l;
+
+	for (l = 0; l < font->height; l++) {
+		dpanic_draw_line(msg, left_margin, l, sb->width, font);
+		if (convert)
+			convert(dpanic_line_buf, dpanic_line_buf, sb->width);
+
+		dst_off = (y * font->height + l) * sb->pitch;
+		iosys_map_memcpy_to(&sb->map, dst_off, dpanic_line_buf,
+				    sb->width * sb->format->cpp[0]);
+	}
+}
+
+static void dpanic_draw_empty_txt_line(size_t y,
+			  struct drm_scanout_buffer *sb,
+			  const struct font_desc *font,
+			  void (*convert)(void *dbuf, const void *sbuf, unsigned int npixels))
+{
+	size_t i, dst_off;
+	u32 *dst = dpanic_line_buf;
+
+	for (i = 0; i < sb->width; i++)
+		*dst++ = bg_color;
+
+	if (convert)
+		convert(dpanic_line_buf, dpanic_line_buf, sb->width);
+
+	for (i = 0; i < font->height; i++) {
+		dst_off = (y * font->height + i) * sb->pitch;
+		iosys_map_memcpy_to(&sb->map, dst_off, dpanic_line_buf,
+				    sb->width * sb->format->cpp[0]);
+	}
+}
+
+static size_t dpanic_needed_lines(size_t chars_per_line)
+{
+	size_t msg_len = ARRAY_SIZE(panic_msg);
+	size_t lines = 0;
+	size_t i;
+
+	for (i = 0; i < msg_len; i++)
+		lines += panic_msg[i].len ? DIV_ROUND_UP(panic_msg[i].len, chars_per_line) : 1;
+	return lines;
+}
+
+static bool dpanic_can_draw_logo(size_t chars_per_line, size_t lines, size_t msg_lines)
+{
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(logo); i++) {
+		if (logo[i].len > chars_per_line)
+			return false;
+	}
+	if (lines < msg_lines + ARRAY_SIZE(logo))
+		return false;
+	return true;
+}
+
+static size_t get_start_line(size_t lines, size_t msg_lines, bool can_draw_logo)
+{
+	size_t remaining;
+	size_t logo_len = ARRAY_SIZE(logo);
+
+	if (lines < msg_lines)
+		return 0;
+	remaining = lines - msg_lines;
+	if (can_draw_logo && remaining / 2 <= logo_len)
+		return logo_len + (remaining - logo_len) / 4;
+	return remaining / 2;
+}
+
+/*
+ * Return the function to convert xrgb8888 to the scanout buffer format
+ * NULL if no conversion is needed, and ERR_PTR if format can't be converted
+ */
+static void (*get_convert_func(const struct drm_format_info *format))
+	    (void *, const void *, unsigned int)
+{
+	switch (format->format) {
+	case DRM_FORMAT_XRGB8888:
+		return NULL;
+	case DRM_FORMAT_RGB565:
+		return drm_fb_xrgb8888_to_rgb565_line;
+	default:
+		return ERR_PTR(EINVAL);
+	}
+}
+
+
+/*
+ * Draw the panic message at the center of the screen
+ */
+static void dpanic_static_draw(struct drm_scanout_buffer *sb, const char *msg)
+{
+	size_t lines, msg_lines, l, msg_start_line, msgi;
+	size_t center, chars_per_line;
+	bool can_draw_logo;
+	struct dpanic_line panic_line;
+	size_t msg_len = ARRAY_SIZE(panic_msg);
+	size_t logo_len = ARRAY_SIZE(logo);
+	void (*convert)(void *dbuf, const void *sbuf, unsigned int npixels);
+	const struct font_desc *font = get_default_font(sb->width, sb->height, 0x8080, 0x8080);
+
+	if (!font)
+		return;
+
+	/* Set the panic reason */
+	panic_msg[msg_len - 1].len = strlen(msg);
+	panic_msg[msg_len - 1].txt = msg;
+
+	lines = sb->height / font->height;
+	chars_per_line = sb->width / font->width;
+
+	msg_lines = dpanic_needed_lines(chars_per_line);
+	can_draw_logo = dpanic_can_draw_logo(chars_per_line, lines, msg_lines);
+	msg_start_line = get_start_line(lines, msg_lines, can_draw_logo);
+
+	convert = get_convert_func(sb->format);
+	if (IS_ERR(convert))
+		return;
+
+	msgi = 0;
+	panic_line.len = 0;
+	for (l = 0; l < lines; l++) {
+		if (can_draw_logo && l < logo_len)
+			dpanic_draw_txt_line(&logo[l], 0, l, sb, font, convert);
+		else if (l >= msg_start_line && msgi < msg_len) {
+			if (!panic_line.len) {
+				panic_line.txt = panic_msg[msgi].txt;
+				panic_line.len = panic_msg[msgi].len;
+			}
+			if (!panic_line.len)
+				dpanic_draw_empty_txt_line(l, sb, font, convert);
+			else {
+				center = panic_line.len > chars_per_line ?
+					 0 : (chars_per_line - panic_line.len) / 2;
+				dpanic_draw_txt_line(&panic_line, center, l, sb, font, convert);
+			}
+			if (panic_line.len > chars_per_line) {
+				panic_line.len -= chars_per_line;
+				panic_line.txt += chars_per_line;
+			} else {
+				panic_line.len = 0;
+				msgi++;
+			}
+		} else {
+			dpanic_draw_empty_txt_line(l, sb, font, convert);
+		}
+	}
+}
+
+static void drm_panic_device(struct drm_device *dev, const char *msg)
+{
+	struct drm_scanout_buffer sb;
+
+	if (dev->driver->get_scanout_buffer(dev, &sb))
+		return;
+	if (!dpanic_line_buf)
+		return;
+
+	/* to avoid buffer overflow on dpanic_line_buf */
+	if (sb.width > DRM_PANIC_MAX_WIDTH)
+		sb.width = DRM_PANIC_MAX_WIDTH;
+
+	dpanic_static_draw(&sb, msg);
+}
+
+static int drm_panic(struct notifier_block *this, unsigned long event,
+		     void *ptr)
+{
+	struct dpanic_drm_device *dpanic_device;
+
+	list_for_each_entry(dpanic_device, &dpanic_devices, head) {
+		drm_panic_device(dpanic_device->dev, ptr);
+	}
+	return NOTIFY_OK;
+}
+
+struct notifier_block drm_panic_notifier = {
+	.notifier_call = drm_panic,
+};
+
+/**
+ * drm_panic_register() - Initialize DRM panic for a device
+ * @dev: the DRM device on which the panic screen will be displayed.
+ */
+void drm_panic_register(struct drm_device *dev)
+{
+	struct dpanic_drm_device *new;
+
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return;
+
+	new->dev = dev;
+	mutex_lock(&dpanic_lock);
+	if (!dpanic_line_buf)
+		dpanic_line_buf = kmalloc(DRM_PANIC_MAX_WIDTH * sizeof(u32), GFP_KERNEL);
+	if (!dpanic_line_buf)
+		goto unlock;
+	list_add_tail(&new->head, &dpanic_devices);
+	drm_info(dev, "Registered with drm panic\n");
+unlock:
+	mutex_unlock(&dpanic_lock);
+}
+EXPORT_SYMBOL(drm_panic_register);
+
+/**
+ * drm_panic_unregister()
+ * @dev: the DRM device previously registered.
+ */
+void drm_panic_unregister(struct drm_device *dev)
+{
+	struct dpanic_drm_device *dpanic_device;
+	struct dpanic_drm_device *found = NULL;
+
+	mutex_lock(&dpanic_lock);
+	list_for_each_entry(dpanic_device, &dpanic_devices, head) {
+		if (dpanic_device->dev == dev)
+			found = dpanic_device;
+	}
+	if (found) {
+		list_del(&found->head);
+		kfree(found);
+		drm_info(dev, "Unregistered with drm panic\n");
+	}
+	if (dpanic_line_buf && list_empty(&dpanic_devices)) {
+		kfree(dpanic_line_buf);
+		dpanic_line_buf = NULL;
+	}
+	mutex_unlock(&dpanic_lock);
+}
+EXPORT_SYMBOL(drm_panic_unregister);
+
+/**
+ * drm_panic_init() - Initialize drm-panic subsystem
+ *
+ * register the panic notifier
+ */
+void drm_panic_init(void)
+{
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &drm_panic_notifier);
+}
+
+/**
+ * drm_log_exit() - Shutdown drm-panic subsystem
+ */
+void drm_panic_exit(void)
+{
+	atomic_notifier_chain_unregister(&panic_notifier_list,
+					 &drm_panic_notifier);
+}
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index 89e2706cac56..e538c87116d3 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -43,6 +43,7 @@ struct dma_buf_attachment;
 struct drm_display_mode;
 struct drm_mode_create_dumb;
 struct drm_printer;
+struct drm_scanout_buffer;
 struct sg_table;
 
 /**
@@ -408,6 +409,19 @@ struct drm_driver {
 	 */
 	void (*show_fdinfo)(struct drm_printer *p, struct drm_file *f);
 
+	/**
+	 * @get_scanout_buffer:
+	 *
+	 * Get the current scanout buffer, to display a panic message with drm_panic.
+	 * It is called from a panic callback, and must follow its restrictions.
+	 *
+	 * Returns:
+	 *
+	 * Zero on success, negative errno on failure.
+	 */
+	int (*get_scanout_buffer)(struct drm_device *dev,
+				  struct drm_scanout_buffer *sb);
+
 	/** @major: driver major number */
 	int major;
 	/** @minor: driver minor number */
diff --git a/include/drm/drm_panic.h b/include/drm/drm_panic.h
new file mode 100644
index 000000000000..db430b8dfbb2
--- /dev/null
+++ b/include/drm/drm_panic.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 or MIT */
+#ifndef __DRM_PANIC_H__
+#define __DRM_PANIC_H__
+
+/*
+ * Copyright (c) 2023 Jocelyn Falempe <jfalempe@redhat.com>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/iosys-map.h>
+
+struct drm_device;
+
+struct drm_scanout_buffer {
+	const struct drm_format_info *format;
+	struct iosys_map map;
+	unsigned int pitch;
+	unsigned int width;
+	unsigned int height;
+};
+
+#ifdef CONFIG_DRM_PANIC
+
+void drm_panic_init(void);
+void drm_panic_exit(void);
+
+void drm_panic_register(struct drm_device *dev);
+void drm_panic_unregister(struct drm_device *dev);
+
+#else
+
+static inline void drm_panic_init(void) {}
+static inline void drm_panic_exit(void) {}
+
+static inline void drm_panic_register(struct drm_device *dev) {}
+static inline void drm_panic_unregister(struct drm_device *dev) {}
+
+#endif
+
+#endif /* __DRM_LOG_H__ */
-- 
2.41.0