[PATCH v7 2/9] drm/panic: Add a drm panic handler
Daniel Vetter
daniel at ffwll.ch
Fri Jan 12 13:31:56 UTC 2024
On Thu, Jan 04, 2024 at 05:00:46PM +0100, Jocelyn Falempe wrote:
> 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.
>
> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
Bunch of comments on the glue, I didn't look at the drawing function in
detail assuming that that's all working :-)
-Sima
> ---
> drivers/gpu/drm/Kconfig | 23 +++
> drivers/gpu/drm/Makefile | 1 +
> drivers/gpu/drm/drm_drv.c | 8 +
> drivers/gpu/drm/drm_panic.c | 369 ++++++++++++++++++++++++++++++++++++
> include/drm/drm_drv.h | 21 ++
> include/drm/drm_panic.h | 97 ++++++++++
> 6 files changed, 519 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 628f90ed8a9b..a8219c98c8d6 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -103,6 +103,29 @@ 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 DRM_KMS_HELPER
> + select FONT_SUPPORT
> + 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.
> + To support Hi-DPI Display, you can enable bigger fonts like
> + FONT_TER16x32
> +
> +config DRM_PANIC_FOREGROUND_COLOR
> + hex "Drm panic screen foreground color, in RGB"
> + depends on DRM_PANIC
> + default 0xffffff
> +
> +config DRM_PANIC_BACKGROUND_COLOR
> + hex "Drm panic screen background color, in RGB"
> + depends on DRM_PANIC
> + default 0x000000
> +
> 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 8ac6f4b9546e..fdf3d3fe0c78 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -60,6 +60,7 @@ drm-$(CONFIG_DRM_PRIVACY_SCREEN) += \
> drm_privacy_screen.o \
> drm_privacy_screen_x86.o
> drm-$(CONFIG_DRM_ACCEL) += ../../accel/drm_accel.o
> +drm-$(CONFIG_DRM_PANIC) += drm_panic.o
> obj-$(CONFIG_DRM) += drm.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 243cacb3575c..998942e6d687 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -43,6 +43,7 @@
> #include <drm/drm_file.h>
> #include <drm/drm_managed.h>
> #include <drm/drm_mode_object.h>
> +#include <drm/drm_panic.h>
> #include <drm/drm_print.h>
> #include <drm/drm_privacy_screen_machine.h>
>
> @@ -944,6 +945,9 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
> goto err_unload;
> }
>
> + if (driver->get_scanout_buffer)
> + drm_panic_register(dev);
> +
> DRM_INFO("Initialized %s %d.%d.%d %s for %s on minor %d\n",
> driver->name, driver->major, driver->minor,
> driver->patchlevel, driver->date,
> @@ -987,6 +991,8 @@ void drm_dev_unregister(struct drm_device *dev)
> {
> dev->registered = false;
>
> + drm_panic_unregister(dev);
> +
> drm_client_dev_unregister(dev);
>
> if (drm_core_check_feature(dev, DRIVER_MODESET))
> @@ -1066,6 +1072,7 @@ 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();
> }
> @@ -1077,6 +1084,7 @@ 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..362a696ec48a
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -0,0 +1,369 @@
> +// SPDX-License-Identifier: GPL-2.0 or MIT
> +/*
> + * Copyright (c) 2023 Red Hat.
> + * Author: Jocelyn Falempe <jfalempe at redhat.com>
> + * inspired by the drm_log driver from David Herrmann <dh.herrmann at 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 handler");
> +MODULE_LICENSE("GPL");
> +
> +/**
> + * DOC: DRM Panic
You need to tie these nice kerneldocs into the overall documentation tree,
or they're not getting built. Please then also check that all the links
and formatting works correctly.
> + *
> + * This module displays a user friendly message on screen when a kernel panic
> + * occurs. This is conflicting with fbcon, so you can only enable it when fbcon
> + * is disabled.
> + * It's intended for end-user, so have minimal technical/debug information.
> + */
> +
> +/*
> + * Implementation details:
> + *
> + * It is a panic handler, so it can't take lock, allocate memory, run tasks/irq,
> + * or attempt to sleep. It's a best effort, and it may not be able to display
> + * the message in all situations (like if the panic occurs in the middle of a
> + * modesetting).
> + * 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 drm_panic_device {
> + struct list_head head;
> + struct drm_device *dev;
> +};
> +
> +struct drm_panic_line {
> + u32 len;
> + const char *txt;
> +};
> +
> +#define PANIC_LINE(s) {.len = sizeof(s) - 1, .txt = s}
> +
> +static struct drm_panic_line panic_msg[] = {
> + PANIC_LINE("KERNEL PANIC !"),
> + PANIC_LINE(""),
> + PANIC_LINE("Please reboot your computer."),
> + PANIC_LINE(""),
> + PANIC_LINE(""), /* overwritten with panic reason */
> +};
> +
> +static const struct drm_panic_line logo[] = {
> + PANIC_LINE(" .--. _"),
> + PANIC_LINE(" |o_o | | |"),
> + PANIC_LINE(" |:_/ | | |"),
> + PANIC_LINE(" // \\ \\ |_|"),
> + PANIC_LINE(" (| | ) _"),
> + PANIC_LINE(" /'\\_ _/`\\ (_)"),
> + PANIC_LINE(" \\___)=(___/"),
> +};
> +
> +static LIST_HEAD(drm_panic_devices);
> +static DEFINE_MUTEX(drm_panic_lock);
> +
> +static void draw_empty_line_map(struct drm_scanout_buffer *sb, size_t top, size_t height, u32 color)
> +{
> + struct iosys_map dst = sb->map;
> +
> + iosys_map_incr(&dst, top * sb->pitch);
> + drm_fb_fill(&dst, sb->pitch, height, sb->width, color, sb->format->cpp[0]);
> +}
> +
> +static void draw_txt_line_map(const struct drm_panic_line *msg, size_t left, size_t top,
> + struct drm_scanout_buffer *sb, u32 fg_color, u32 bg_color,
> + const struct font_desc *font)
> +{
> + size_t i;
> + const u8 *src;
> + size_t src_stride = DIV_ROUND_UP(font->width, 8);
> + struct iosys_map dst = sb->map;
> + size_t end_text;
> + unsigned int px_width = sb->format->cpp[0];
> +
> + iosys_map_incr(&dst, top * sb->pitch);
> + drm_fb_fill(&dst, sb->pitch, font->height, left, bg_color, px_width);
> + iosys_map_incr(&dst, left * px_width);
> + for (i = 0; i < msg->len; i++) {
> + src = font->data + (msg->txt[i] * font->height) * src_stride;
> + drm_fb_blit_from_r1(&dst, sb->pitch, src, src_stride, font->height, font->width,
> + fg_color, bg_color, px_width);
> + iosys_map_incr(&dst, font->width * px_width);
> + }
> + end_text = (msg->len * font->width) + left;
> + if (sb->width > end_text)
> + drm_fb_fill(&dst, sb->pitch, font->height, sb->width - end_text,
> + bg_color, px_width);
> +}
> +
> +static void draw_empty_line_px(struct drm_scanout_buffer *sb, size_t top, size_t height, u32 color)
> +{
> + unsigned int x, y;
> +
> + for (y = 0; y < height; y++)
> + for (x = 0; x < sb->width; x++)
> + sb->draw_pixel_xy(x, y + top, color, sb->private);
> +}
> +
> +static void draw_txt_line_px(const struct drm_panic_line *msg, size_t left, size_t top,
> + struct drm_scanout_buffer *sb, u32 fg_color, u32 bg_color,
> + const struct font_desc *font)
> +{
> + unsigned int x, y, i;
> + const u8 *src;
> + u32 color;
> + size_t src_stride = DIV_ROUND_UP(font->width, 8);
> + size_t end_text = msg->len * font->width + left;
> + size_t right = sb->width > end_text ? sb->width - end_text : 0;
> +
> + for (y = 0; y < font->height; y++) {
> + for (x = 0; x < left; x++)
> + sb->draw_pixel_xy(x, y + top, bg_color, sb->private);
> +
> + for (i = 0; i < msg->len; i++) {
> + src = font->data + (msg->txt[i] * font->height + y) * src_stride;
> + for (x = 0; x < font->width; x++) {
> + color = (src[x / 8] & (0x80 >> (x % 8))) ? fg_color : bg_color;
> + sb->draw_pixel_xy(x + left + font->width * i, y + top, color,
> + sb->private);
> + }
> + }
> +
> + for (x = 0; x < right; x++)
> + sb->draw_pixel_xy(x + end_text, y + top, bg_color, sb->private);
> + }
> +}
> +
> +static void draw_empty_line(struct drm_scanout_buffer *sb, size_t top, size_t height, u32 color)
> +{
> + if (sb->draw_pixel_xy)
> + draw_empty_line_px(sb, top, height, color);
> + else
> + draw_empty_line_map(sb, top, height, color);
> +}
> +
> +static void draw_txt_line(const struct drm_panic_line *msg, size_t left, size_t top,
> + struct drm_scanout_buffer *sb, u32 fg_color, u32 bg_color,
> + const struct font_desc *font)
> +{
> + if (sb->draw_pixel_xy)
> + draw_txt_line_px(msg, left, top, sb, fg_color, bg_color, font);
> + else
> + draw_txt_line_map(msg, left, top, sb, fg_color, bg_color, font);
> +}
> +
> +
> +static size_t panic_msg_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 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 draw_logo)
> +{
> + size_t remaining;
> + size_t logo_len = ARRAY_SIZE(logo);
> +
> + if (lines < msg_lines)
> + return 0;
> + remaining = lines - msg_lines;
> + if (draw_logo && remaining / 2 <= logo_len)
> + return logo_len + (remaining - logo_len) / 4;
> + return remaining / 2;
> +}
> +
> +/*
> + * Draw the panic message at the center of the screen
> + */
> +static void draw_panic_static(struct drm_scanout_buffer *sb, const char *msg)
> +{
> + size_t lines, msg_lines, l, msg_start_line, remaining, msgi;
> + size_t chars_per_line;
> + bool draw_logo;
> + struct drm_panic_line panic_line;
> + size_t msg_len = ARRAY_SIZE(panic_msg);
> + size_t logo_len = ARRAY_SIZE(logo);
> + u32 fg_color = CONFIG_DRM_PANIC_FOREGROUND_COLOR;
> + u32 bg_color = CONFIG_DRM_PANIC_BACKGROUND_COLOR;
> + 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 = panic_msg_needed_lines(chars_per_line);
> + draw_logo = can_draw_logo(chars_per_line, lines, msg_lines);
> + msg_start_line = get_start_line(lines, msg_lines, draw_logo);
> +
> + fg_color = drm_fb_convert_from_xrgb8888(fg_color, sb->format->format);
> + bg_color = drm_fb_convert_from_xrgb8888(bg_color, sb->format->format);
> +
> + msgi = 0;
> + panic_line.len = 0;
> + for (l = 0; l < lines; l++) {
> + if (draw_logo && l < logo_len)
> + draw_txt_line(&logo[l], 0, l * font->height, sb, fg_color, bg_color, font);
> + 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) {
> + draw_empty_line(sb, l * font->height, font->height, bg_color);
> + msgi++;
> + } else if (panic_line.len > chars_per_line) {
> + remaining = panic_line.len - chars_per_line;
> + panic_line.len = chars_per_line;
> + draw_txt_line(&panic_line, 0, l * font->height, sb, fg_color,
> + bg_color, font);
> + panic_line.txt += chars_per_line;
> + panic_line.len = remaining;
> + } else {
> + draw_txt_line(&panic_line,
> + font->width * (chars_per_line - panic_line.len) / 2,
> + l * font->height, sb, fg_color, bg_color, font);
> + panic_line.len = 0;
> + msgi++;
> + }
> + } else {
> + draw_empty_line(sb, l * font->height, font->height, bg_color);
> + }
> + }
> + /* Fill the bottom of the screen, if sb->height is not a multiple of font->height */
> + if (sb->height % font->height)
> + draw_empty_line(sb, l * font->height, sb->height - l * font->height, bg_color);
> +}
> +
> +static void draw_panic_device(struct drm_device *dev, const char *msg)
> +{
> + struct drm_scanout_buffer sb = {0};
> +
> + if (dev->driver->get_scanout_buffer(dev, &sb))
> + return;
> + draw_panic_static(&sb, msg);
> + if (sb.flush)
> + sb.flush(sb.private);
> +}
> +
> +static int drm_panic(struct notifier_block *this, unsigned long event,
> + void *ptr)
> +{
> + struct drm_panic_device *drm_panic_device;
> +
> + list_for_each_entry(drm_panic_device, &drm_panic_devices, head) {
> + draw_panic_device(drm_panic_device->dev, ptr);
The locking here is busted. Which is why the atomic notifier chain is
special and uses atomic semantics - I would just avoid this issue and
directly register each drm_panic_device instead of trying to maintain a
drm-local list and getting the locking rules wrong.
> + }
> + return NOTIFY_OK;
> +}
> +
> +static 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 drm_panic_device *new;
> +
> + new = kzalloc(sizeof(*new), GFP_KERNEL);
> + if (!new)
> + return;
> +
> + new->dev = dev;
> + mutex_lock(&drm_panic_lock);
> + list_add_tail(&new->head, &drm_panic_devices);
> + mutex_unlock(&drm_panic_lock);
> +
> + drm_info(dev, "Registered with drm panic\n");
> +}
> +EXPORT_SYMBOL(drm_panic_register);
> +
> +/**
> + * drm_panic_unregister()
> + * @dev: the DRM device previously registered.
> + */
> +void drm_panic_unregister(struct drm_device *dev)
> +{
> + struct drm_panic_device *drm_panic_device;
> + struct drm_panic_device *found = NULL;
> +
> + mutex_lock(&drm_panic_lock);
> + list_for_each_entry(drm_panic_device, &drm_panic_devices, head) {
Can't we just store a pointer in drm_device (or embed the entire thing
outright) instead of this dance?
> + if (drm_panic_device->dev == dev)
> + found = drm_panic_device;
> + }
> + if (found) {
> + list_del(&found->head);
> + kfree(found);
> + drm_info(dev, "Unregistered with drm panic\n");
> + }
> + mutex_unlock(&drm_panic_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_panic_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 8878260d7529..99e5bcf13975 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;
>
> /**
> @@ -401,6 +402,26 @@ 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.
> + * The driver should do the minimum changes to provide a linear buffer, that
> + * can be used to display the panic screen.
> + * It is called from a panic callback, and must follow its restrictions.
> + * (no locks, no memory allocation, no sleep, no thread/workqueue, ...)
> + * It's a best effort mode, so it's expected that in some complex cases the
> + * panic screen won't be displayed.
> + * Some hardware cannot provide a linear buffer, so there is a draw_pixel_xy()
> + * callback in the struct drm_scanout_buffer that can be used in this case.
I'd move this to the documentation of drm_scanout_buffer and just put a
kernel-doc hyperlink in here referencing that for further information.
> + *
> + * Returns:
> + *
> + * Zero on success, negative errno on failure.
> + */
> + int (*get_scanout_buffer)(struct drm_device *dev,
> + struct drm_scanout_buffer *sb);
Please put this hook into drm_mode_config_funcs and not into the overall
drm_driver struct. At least for kms we're trying to keep a clean design
(and I know that stuff like dumb buffers got misplaced, not a good reason
to do it again ...).
> +
> /** @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..bcf392b6fa1b
> --- /dev/null
> +++ b/include/drm/drm_panic.h
> @@ -0,0 +1,97 @@
> +/* SPDX-License-Identifier: GPL-2.0 or MIT */
> +#ifndef __DRM_PANIC_H__
> +#define __DRM_PANIC_H__
> +
> +/*
> + * Copyright (c) 2023 Red Hat.
> + * Author: Jocelyn Falempe <jfalempe at redhat.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/iosys-map.h>
> +
> +struct drm_device;
> +
> +/**
> + * struct drm_scanout_buffer - DRM scanout buffer
> + *
> + * This structure holds the information necessary for drm_panic to draw the
> + * panic screen, and display it.
> + * If the driver can't provide a linear buffer, it must clear @map with
> + * iosys_map_clear() and provide a draw_pixel_xy() function.
I think it's better to move this to the documentation of @map and
@draw_pixel_xy.
> + */
> +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
The should here is confusing, because it's an either/or.
> + * sent to the display hardware. Tearing is not an issue for the panic
> + * screen.
> + */
> + struct iosys_map map;
I think you're a bit unclear on whether you allow non-null @map for the
case when @draw_pixel_xy is set. Current docs says it's either/or, but you
don't have any checks for iosys_map_is_null(). I'd add something like
WARN_ON(sb->draw_pixel_xy && !iosys_map_is_null(sb->map));
right after the call to ->get_scanout_buffer to lock down this rule.
> + /**
> + * @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;
> + /**
> + * @private:
> + *
> + * In case the driver can't provide a linear buffer, this is a pointer to
> + * some private data, that will be passed when calling @draw_pixel_xy()
> + * and @flush()
> + */
> + void *private;
> + /**
> + * @draw_pixel_xy:
> + *
> + * In case the driver can't provide a linear buffer, this is a function
> + * that drm_panic will call for each pixel to draw.
> + * Color will be converted to the format specified by @format.
> + */
> + void (*draw_pixel_xy)(unsigned int x, unsigned int y, u32 color, void *private);
> + /**
> + * @flush:
> + *
> + * This function is called after the panic screen is drawn, either using
> + * the iosys_map or the draw_pixel_xy path. In this function, the driver
> + * can send additional commands to the hardware, to make the buffer
> + * visible.
Uh how does flush work for the @map path? I'd just pass the overall
drm_scanout_buffer struct to both of these hooks as the first parameter
and let the driver figure out what it needs.
> + */
> + void (*flush)(void *private);
> +};
> +
> +#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_PANIC_H__ */
> --
> 2.43.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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