[v9,2/6] drm/log: Introduce a new boot logger to draw the kmsg on the screen

Commit Message

Jocelyn Falempe Dec. 4, 2024, 3:45 p.m. UTC

drm_log is a simple logger that uses the drm_client API to print the
kmsg boot log on the screen. This is not a full replacement to fbcon,
as it will only print the kmsg. It will never handle user input, or a
terminal because this is better done in userspace.

Design decisions:
 * It uses the drm_client API, so it should work on all drm drivers
   from the start.
 * It doesn't scroll the message, that way it doesn't need to redraw
   the whole screen for each new message.
   It also means it doesn't have to keep drawn messages in memory, to
   redraw them when scrolling.
 * It uses the new non-blocking console API, so it should work well
   with PREEMPT_RT.

This patch also adds a Kconfig menu to select the drm client to use.
It can be overwritten on the kernel command line with:
drm_client_lib.active=log or drm_client_lib.active=fbdev

Signed-off-by: Jocelyn Falempe <[e-mail]>
Reviewed-by: John Ogness <[e-mail]> # console API
---

v2:
 * Use vmap_local() api, with that change, I've tested it successfully on simpledrm, virtio-gpu, amdgpu, and nouveau.
 * Stop drawing when the drm_master is taken. This avoid wasting CPU cycle if the buffer is not visible.
 * Use deferred probe. Only do the probe the first time there is a log to draw. With this, if you boot with quiet, drm_log won't do any modeset.
 * Add color support for the timestamp prefix, like what dmesg does.
 * Add build dependency on  disabling the fbdev emulation, as they are both drm_client, and there is no way to choose which one gets the focus.

v3:
 * Remove the work thread and circular buffer, and use the new write_thread() console API.
 * Register a console for each drm driver.

v4:
 * Can be built as a module, even if that's not really useful.
 * Rebased on top of "drm: Introduce DRM client library" series from Thomas Zimmermann.
 * Add a Kconfig menu to choose between drm client.
 
v5:
 * Build drm_log in drm_client_lib module, to avoid circular dependency. 

v8:
 * Rebased after drm client moved to drivers/gpu/drm/clients/
 * Rename DRM_LOG to DRM_CLIENT_LOG (Thomas Zimmermann)
 * Add an info message if no clients are initialized in drm_client_setup()
 
v9:
 * Add cflags to remove the "../" when including drm internal headers (Jani Nikula)
 * Order select alphabetically in KConfig (Thomas Zimmermann)
 * Replace drm_info with drm_dbg, to be less verbose (Thomas Zimmermann)
 * Rename module parameter to drm_client_lib.active (Thomas Zimmermann)
 * Warn if drm_client_lib.active is malformated (Thomas Zimmermann)
 
 drivers/gpu/drm/clients/Kconfig               |  48 +++
 drivers/gpu/drm/clients/Makefile              |   3 +
 drivers/gpu/drm/clients/drm_client_internal.h |   6 +
 drivers/gpu/drm/clients/drm_client_setup.c    |  29 +-
 drivers/gpu/drm/clients/drm_log.c             | 370 ++++++++++++++++++
 5 files changed, 452 insertions(+), 4 deletions(-)
 create mode 100644 drivers/gpu/drm/clients/drm_log.c

Comments

Thomas Zimmermann Dec. 5, 2024, 4:21 p.m. UTC | #1

Am 04.12.24 um 16:45 schrieb Jocelyn Falempe:
> drm_log is a simple logger that uses the drm_client API to print the
> kmsg boot log on the screen. This is not a full replacement to fbcon,
> as it will only print the kmsg. It will never handle user input, or a
> terminal because this is better done in userspace.
>
> Design decisions:
>   * It uses the drm_client API, so it should work on all drm drivers
>     from the start.
>   * It doesn't scroll the message, that way it doesn't need to redraw
>     the whole screen for each new message.
>     It also means it doesn't have to keep drawn messages in memory, to
>     redraw them when scrolling.
>   * It uses the new non-blocking console API, so it should work well
>     with PREEMPT_RT.
>
> This patch also adds a Kconfig menu to select the drm client to use.
> It can be overwritten on the kernel command line with:
> drm_client_lib.active=log or drm_client_lib.active=fbdev
>
> Signed-off-by: Jocelyn Falempe <[e-mail]>
> Reviewed-by: John Ogness <[e-mail]> # console API

Reviewed-by: Thomas Zimmermann <[e-mail]>

> ---
>
> v2:
>   * Use vmap_local() api, with that change, I've tested it successfully on simpledrm, virtio-gpu, amdgpu, and nouveau.
>   * Stop drawing when the drm_master is taken. This avoid wasting CPU cycle if the buffer is not visible.
>   * Use deferred probe. Only do the probe the first time there is a log to draw. With this, if you boot with quiet, drm_log won't do any modeset.
>   * Add color support for the timestamp prefix, like what dmesg does.
>   * Add build dependency on  disabling the fbdev emulation, as they are both drm_client, and there is no way to choose which one gets the focus.
>
> v3:
>   * Remove the work thread and circular buffer, and use the new write_thread() console API.
>   * Register a console for each drm driver.
>
> v4:
>   * Can be built as a module, even if that's not really useful.
>   * Rebased on top of "drm: Introduce DRM client library" series from Thomas Zimmermann.
>   * Add a Kconfig menu to choose between drm client.
>   
> v5:
>   * Build drm_log in drm_client_lib module, to avoid circular dependency.
>
> v8:
>   * Rebased after drm client moved to drivers/gpu/drm/clients/
>   * Rename DRM_LOG to DRM_CLIENT_LOG (Thomas Zimmermann)
>   * Add an info message if no clients are initialized in drm_client_setup()
>   
> v9:
>   * Add cflags to remove the "../" when including drm internal headers (Jani Nikula)
>   * Order select alphabetically in KConfig (Thomas Zimmermann)
>   * Replace drm_info with drm_dbg, to be less verbose (Thomas Zimmermann)
>   * Rename module parameter to drm_client_lib.active (Thomas Zimmermann)
>   * Warn if drm_client_lib.active is malformated (Thomas Zimmermann)
>   
>   drivers/gpu/drm/clients/Kconfig               |  48 +++
>   drivers/gpu/drm/clients/Makefile              |   3 +
>   drivers/gpu/drm/clients/drm_client_internal.h |   6 +
>   drivers/gpu/drm/clients/drm_client_setup.c    |  29 +-
>   drivers/gpu/drm/clients/drm_log.c             | 370 ++++++++++++++++++
>   5 files changed, 452 insertions(+), 4 deletions(-)
>   create mode 100644 drivers/gpu/drm/clients/drm_log.c
>
> diff --git a/drivers/gpu/drm/clients/Kconfig b/drivers/gpu/drm/clients/Kconfig
> index 01ad3b000130..c18decc90200 100644
> --- a/drivers/gpu/drm/clients/Kconfig
> +++ b/drivers/gpu/drm/clients/Kconfig
> @@ -12,6 +12,7 @@ config DRM_CLIENT_LIB
>   config DRM_CLIENT_SELECTION
>   	tristate
>   	depends on DRM
> +	select DRM_CLIENT_LIB if DRM_CLIENT_LOG
>   	select DRM_CLIENT_LIB if DRM_FBDEV_EMULATION
>   	help
>   	  Drivers that support in-kernel DRM clients have to select this
> @@ -70,4 +71,51 @@ config DRM_FBDEV_LEAK_PHYS_SMEM
>   	  If in doubt, say "N" or spread the word to your closed source
>   	  library vendor.
>   
> +config DRM_CLIENT_LOG
> +	bool "Print the kernel boot message on the screen"
> +	depends on DRM_CLIENT_SELECTION
> +	select DRM_CLIENT
> +	select DRM_CLIENT_SETUP
> +	select DRM_DRAW
> +	help
> +	  This enable a drm logger, that will print the kernel messages to the
> +	  screen until the userspace is ready to take over.
> +
> +	  If you only need logs, but no terminal, or if you prefer userspace
> +	  terminal, say "Y".
> +
> +choice
> +	prompt "Default DRM Client"
> +	depends on DRM_CLIENT_SELECTION
> +	default DRM_CLIENT_DEFAULT_FBDEV
> +	help
> +	  Selects the default drm client.
> +
> +	  The selection made here can be overridden by using the kernel
> +	  command line 'drm_client_lib.active=fbdev' option.
> +
> +config DRM_CLIENT_DEFAULT_FBDEV
> +	bool "fbdev"
> +	depends on DRM_FBDEV_EMULATION
> +	help
> +	  Use fbdev emulation as default drm client. This is needed to have
> +	  fbcon on top of a drm driver.
> +
> +config DRM_CLIENT_DEFAULT_LOG
> +	bool "log"
> +	depends on DRM_CLIENT_LOG
> +	help
> +	  Use drm log as default drm client. This will display boot logs on the
> +	  screen, but doesn't implement a full terminal. For that you will need
> +	  a userspace terminal using drm/kms.
> +
> +endchoice
> +
> +config DRM_CLIENT_DEFAULT
> +       string
> +       depends on DRM_CLIENT
> +       default "fbdev" if DRM_CLIENT_DEFAULT_FBDEV
> +       default "log" if DRM_CLIENT_DEFAULT_LOG
> +       default ""
> +
>   endmenu
> diff --git a/drivers/gpu/drm/clients/Makefile b/drivers/gpu/drm/clients/Makefile
> index 1d004ec92e1e..c16addbc327f 100644
> --- a/drivers/gpu/drm/clients/Makefile
> +++ b/drivers/gpu/drm/clients/Makefile
> @@ -1,5 +1,8 @@
>   # SPDX-License-Identifier: GPL-2.0
>   
> +subdir-ccflags-y += -I$(src)/..
> +
>   drm_client_lib-y := drm_client_setup.o
> +drm_client_lib-$(CONFIG_DRM_CLIENT_LOG) += drm_log.o
>   drm_client_lib-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fbdev_client.o
>   obj-$(CONFIG_DRM_CLIENT_LIB) += drm_client_lib.o
> diff --git a/drivers/gpu/drm/clients/drm_client_internal.h b/drivers/gpu/drm/clients/drm_client_internal.h
> index 23258934956a..6dc078bf6503 100644
> --- a/drivers/gpu/drm/clients/drm_client_internal.h
> +++ b/drivers/gpu/drm/clients/drm_client_internal.h
> @@ -16,4 +16,10 @@ static inline int drm_fbdev_client_setup(struct drm_device *dev,
>   }
>   #endif
>   
> +#ifdef CONFIG_DRM_CLIENT_LOG
> +void drm_log_register(struct drm_device *dev);
> +#else
> +static inline void drm_log_register(struct drm_device *dev) {}
> +#endif
> +
>   #endif
> diff --git a/drivers/gpu/drm/clients/drm_client_setup.c b/drivers/gpu/drm/clients/drm_client_setup.c
> index 4b211a4812b5..e17265039ca8 100644
> --- a/drivers/gpu/drm/clients/drm_client_setup.c
> +++ b/drivers/gpu/drm/clients/drm_client_setup.c
> @@ -7,6 +7,12 @@
>   
>   #include "drm_client_internal.h"
>   
> +static char drm_client_default[16] = CONFIG_DRM_CLIENT_DEFAULT;
> +module_param_string(active, drm_client_default, sizeof(drm_client_default), 0444);
> +MODULE_PARM_DESC(active,
> +		 "Choose which drm client to start, default is"
> +		 CONFIG_DRM_CLIENT_DEFAULT "]");
> +
>   /**
>    * drm_client_setup() - Setup in-kernel DRM clients
>    * @dev: DRM device
> @@ -25,11 +31,26 @@
>    */
>   void drm_client_setup(struct drm_device *dev, const struct drm_format_info *format)
>   {
> -	int ret;
>   
> -	ret = drm_fbdev_client_setup(dev, format);
> -	if (ret)
> -		drm_warn(dev, "Failed to set up DRM client; error %d\n", ret);
> +#ifdef CONFIG_DRM_FBDEV_EMULATION
> +	if (!strcmp(drm_client_default, "fbdev")) {
> +		int ret;
> +
> +		ret = drm_fbdev_client_setup(dev, format);
> +		if (ret)
> +			drm_warn(dev, "Failed to set up DRM client; error %d\n", ret);
> +		return;
> +	}
> +#endif
> +
> +#ifdef CONFIG_DRM_CLIENT_LOG
> +	if (!strcmp(drm_client_default, "log")) {
> +		drm_log_register(dev);
> +		return;
> +	}
> +#endif
> +	if (strcmp(drm_client_default, ""))
> +		drm_warn(dev, "Unknown DRM client %s\n", drm_client_default);
>   }
>   EXPORT_SYMBOL(drm_client_setup);
>   
> diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
> new file mode 100644
> index 000000000000..4e07bff6c864
> --- /dev/null
> +++ b/drivers/gpu/drm/clients/drm_log.c
> @@ -0,0 +1,370 @@
> +// SPDX-License-Identifier: GPL-2.0 or MIT
> +/*
> + * Copyright (c) 2024 Red Hat.
> + * Author: Jocelyn Falempe <[e-mail]>
> + */
> +
> +#include <linux/console.h>
> +#include <linux/font.h>
> +#include <linux/init.h>
> +#include <linux/iosys-map.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +
> +#include <drm/drm_client.h>
> +#include <drm/drm_drv.h>
> +#include <drm/drm_fourcc.h>
> +#include <drm/drm_framebuffer.h>
> +#include <drm/drm_print.h>
> +
> +#include "drm_client_internal.h"
> +#include "drm_draw_internal.h"
> +
> +MODULE_AUTHOR("Jocelyn Falempe");
> +MODULE_DESCRIPTION("DRM boot logger");
> +MODULE_LICENSE("GPL");
> +
> +/**
> + * DOC: overview
> + *
> + * This is a simple graphic logger, to print the kernel message on screen, until
> + * a userspace application is able to take over.
> + * It is only for debugging purpose.
> + */
> +
> +struct drm_log_scanout {
> +	struct drm_client_buffer *buffer;
> +	const struct font_desc *font;
> +	u32 rows;
> +	u32 columns;
> +	u32 line;
> +	u32 format;
> +	u32 px_width;
> +	u32 front_color;
> +};
> +
> +struct drm_log {
> +	struct mutex lock;
> +	struct drm_client_dev client;
> +	struct console con;
> +	bool probed;
> +	u32 n_scanout;
> +	struct drm_log_scanout *scanout;
> +};
> +
> +static struct drm_log *client_to_drm_log(struct drm_client_dev *client)
> +{
> +	return container_of(client, struct drm_log, client);
> +}
> +
> +static struct drm_log *console_to_drm_log(struct console *con)
> +{
> +	return container_of(con, struct drm_log, con);
> +}
> +
> +static void drm_log_blit(struct iosys_map *dst, unsigned int dst_pitch,
> +			 const u8 *src, unsigned int src_pitch,
> +			 u32 height, u32 width, u32 scale, u32 px_width, u32 color)
> +{
> +	switch (px_width) {
> +	case 2:
> +		drm_draw_blit16(dst, dst_pitch, src, src_pitch, height, width, scale, color);
> +		break;
> +	case 3:
> +		drm_draw_blit24(dst, dst_pitch, src, src_pitch, height, width, scale, color);
> +		break;
> +	case 4:
> +		drm_draw_blit32(dst, dst_pitch, src, src_pitch, height, width, scale, color);
> +		break;
> +	default:
> +		WARN_ONCE(1, "Can't blit with pixel width %d\n", px_width);
> +	}
> +}
> +
> +static void drm_log_clear_line(struct drm_log_scanout *scanout, u32 line)
> +{
> +	struct drm_framebuffer *fb = scanout->buffer->fb;
> +	unsigned long height = scanout->font->height;
> +	struct iosys_map map;
> +	struct drm_rect r = DRM_RECT_INIT(0, line * height, fb->width, height);
> +
> +	if (drm_client_buffer_vmap_local(scanout->buffer, &map))
> +		return;
> +	iosys_map_memset(&map, r.y1 * fb->pitches[0], 0, height * fb->pitches[0]);
> +	drm_client_buffer_vunmap_local(scanout->buffer);
> +	drm_client_framebuffer_flush(scanout->buffer, &r);
> +}
> +
> +static void drm_log_draw_line(struct drm_log_scanout *scanout, const char *s,
> +			      unsigned int len)
> +{
> +	struct drm_framebuffer *fb = scanout->buffer->fb;
> +	struct iosys_map map;
> +	const struct font_desc *font = scanout->font;
> +	size_t font_pitch = DIV_ROUND_UP(font->width, 8);
> +	const u8 *src;
> +	u32 px_width = fb->format->cpp[0];
> +	struct drm_rect r = DRM_RECT_INIT(0, scanout->line * font->height,
> +					  fb->width, (scanout->line + 1) * font->height);
> +	u32 i;
> +
> +	if (drm_client_buffer_vmap_local(scanout->buffer, &map))
> +		return;
> +
> +	iosys_map_incr(&map, r.y1 * fb->pitches[0]);
> +	for (i = 0; i < len && i < scanout->columns; i++) {
> +		src = drm_draw_get_char_bitmap(font, s[i], font_pitch);
> +		drm_log_blit(&map, fb->pitches[0], src, font_pitch, font->height, font->width,
> +			     1, px_width, scanout->front_color);
> +		iosys_map_incr(&map, font->width * px_width);
> +	}
> +
> +	scanout->line++;
> +	if (scanout->line >= scanout->rows)
> +		scanout->line = 0;
> +	drm_client_buffer_vunmap_local(scanout->buffer);
> +	drm_client_framebuffer_flush(scanout->buffer, &r);
> +}
> +
> +static void drm_log_draw_new_line(struct drm_log_scanout *scanout,
> +				  const char *s, unsigned int len)
> +{
> +	if (scanout->line == 0) {
> +		drm_log_clear_line(scanout, 0);
> +		drm_log_clear_line(scanout, 1);
> +		drm_log_clear_line(scanout, 2);
> +	} else if (scanout->line + 2 < scanout->rows)
> +		drm_log_clear_line(scanout, scanout->line + 2);
> +
> +	drm_log_draw_line(scanout, s, len);
> +}
> +
> +static void drm_log_draw_kmsg_record(struct drm_log_scanout *scanout,
> +				     const char *s, unsigned int len)
> +{
> +	/* do not print the ending \n character */
> +	if (s[len - 1] == '\n')
> +		len--;
> +
> +	while (len > scanout->columns) {
> +		drm_log_draw_new_line(scanout, s, scanout->columns);
> +		s += scanout->columns;
> +		len -= scanout->columns;
> +	}
> +	if (len)
> +		drm_log_draw_new_line(scanout, s, len);
> +}
> +
> +static u32 drm_log_find_usable_format(struct drm_plane *plane)
> +{
> +	int i;
> +
> +	for (i = 0; i < plane->format_count; i++)
> +		if (drm_draw_color_from_xrgb8888(0xffffff, plane->format_types[i]) != 0)
> +			return plane->format_types[i];
> +	return DRM_FORMAT_INVALID;
> +}
> +
> +static int drm_log_setup_modeset(struct drm_client_dev *client,
> +				 struct drm_mode_set *mode_set,
> +				 struct drm_log_scanout *scanout)
> +{
> +	struct drm_crtc *crtc = mode_set->crtc;
> +	u32 width = mode_set->mode->hdisplay;
> +	u32 height = mode_set->mode->vdisplay;
> +	u32 format;
> +
> +	scanout->font = get_default_font(width, height, NULL, NULL);
> +	if (!scanout->font)
> +		return -ENOENT;
> +
> +	format = drm_log_find_usable_format(crtc->primary);
> +	if (format == DRM_FORMAT_INVALID)
> +		return -EINVAL;
> +
> +	scanout->buffer = drm_client_framebuffer_create(client, width, height, format);
> +	if (IS_ERR(scanout->buffer)) {
> +		drm_warn(client->dev, "drm_log can't create framebuffer %d %d %p4cc\n",
> +			 width, height, &format);
> +		return -ENOMEM;
> +	}
> +	mode_set->fb = scanout->buffer->fb;
> +	scanout->rows = height / scanout->font->height;
> +	scanout->columns = width / scanout->font->width;
> +	scanout->front_color = drm_draw_color_from_xrgb8888(0xffffff, format);
> +	return 0;
> +}
> +
> +static int drm_log_count_modeset(struct drm_client_dev *client)
> +{
> +	struct drm_mode_set *mode_set;
> +	int count = 0;
> +
> +	mutex_lock(&client->modeset_mutex);
> +	drm_client_for_each_modeset(mode_set, client)
> +		count++;
> +	mutex_unlock(&client->modeset_mutex);
> +	return count;
> +}
> +
> +static void drm_log_init_client(struct drm_log *dlog)
> +{
> +	struct drm_client_dev *client = &dlog->client;
> +	struct drm_mode_set *mode_set;
> +	int i, max_modeset;
> +	int n_modeset = 0;
> +
> +	dlog->probed = true;
> +
> +	if (drm_client_modeset_probe(client, 0, 0))
> +		return;
> +
> +	max_modeset = drm_log_count_modeset(client);
> +	if (!max_modeset)
> +		return;
> +
> +	dlog->scanout = kcalloc(max_modeset, sizeof(*dlog->scanout), GFP_KERNEL);
> +	if (!dlog->scanout)
> +		return;
> +
> +	mutex_lock(&client->modeset_mutex);
> +	drm_client_for_each_modeset(mode_set, client) {
> +		if (!mode_set->mode)
> +			continue;
> +		if (drm_log_setup_modeset(client, mode_set, &dlog->scanout[n_modeset]))
> +			continue;
> +		n_modeset++;
> +	}
> +	mutex_unlock(&client->modeset_mutex);
> +	if (n_modeset == 0)
> +		goto err_nomodeset;
> +
> +	if (drm_client_modeset_commit(client))
> +		goto err_failed_commit;
> +
> +	dlog->n_scanout = n_modeset;
> +	return;
> +
> +err_failed_commit:
> +	for (i = 0; i < n_modeset; i++)
> +		drm_client_framebuffer_delete(dlog->scanout[i].buffer);
> +
> +err_nomodeset:
> +	kfree(dlog->scanout);
> +	dlog->scanout = NULL;
> +}
> +
> +static void drm_log_free_scanout(struct drm_client_dev *client)
> +{
> +	struct drm_log *dlog = client_to_drm_log(client);
> +	int i;
> +
> +	if (dlog->n_scanout) {
> +		for (i = 0; i < dlog->n_scanout; i++)
> +			drm_client_framebuffer_delete(dlog->scanout[i].buffer);
> +		dlog->n_scanout = 0;
> +		kfree(dlog->scanout);
> +		dlog->scanout = NULL;
> +	}
> +}
> +
> +static void drm_log_client_unregister(struct drm_client_dev *client)
> +{
> +	struct drm_log *dlog = client_to_drm_log(client);
> +	struct drm_device *dev = client->dev;
> +
> +	unregister_console(&dlog->con);
> +
> +	mutex_lock(&dlog->lock);
> +	drm_log_free_scanout(client);
> +	drm_client_release(client);
> +	mutex_unlock(&dlog->lock);
> +	kfree(dlog);
> +	drm_dbg(dev, "Unregistered with drm log\n");
> +}
> +
> +static int drm_log_client_hotplug(struct drm_client_dev *client)
> +{
> +	struct drm_log *dlog = client_to_drm_log(client);
> +
> +	mutex_lock(&dlog->lock);
> +	drm_log_free_scanout(client);
> +	dlog->probed = false;
> +	mutex_unlock(&dlog->lock);
> +	return 0;
> +}
> +
> +static const struct drm_client_funcs drm_log_client_funcs = {
> +	.owner		= THIS_MODULE,
> +	.unregister	= drm_log_client_unregister,
> +	.hotplug	= drm_log_client_hotplug,
> +};
> +
> +static void drm_log_write_thread(struct console *con, struct nbcon_write_context *wctxt)
> +{
> +	struct drm_log *dlog = console_to_drm_log(con);
> +	int i;
> +
> +	if (!dlog->probed)
> +		drm_log_init_client(dlog);
> +
> +	for (i = 0; i < dlog->n_scanout; i++)
> +		drm_log_draw_kmsg_record(&dlog->scanout[i], wctxt->outbuf, wctxt->len);
> +}
> +
> +static void drm_log_lock(struct console *con, unsigned long *flags)
> +{
> +	struct drm_log *dlog = console_to_drm_log(con);
> +
> +	mutex_lock(&dlog->lock);
> +	migrate_disable();
> +}
> +
> +static void drm_log_unlock(struct console *con, unsigned long flags)
> +{
> +	struct drm_log *dlog = console_to_drm_log(con);
> +
> +	migrate_enable();
> +	mutex_unlock(&dlog->lock);
> +}
> +
> +static void drm_log_register_console(struct console *con)
> +{
> +	strscpy(con->name, "drm_log");
> +	con->write_thread = drm_log_write_thread;
> +	con->device_lock = drm_log_lock;
> +	con->device_unlock = drm_log_unlock;
> +	con->flags = CON_PRINTBUFFER | CON_NBCON;
> +	con->index = -1;
> +
> +	register_console(con);
> +}
> +
> +/**
> + * drm_log_register() - Register a drm device to drm_log
> + * @dev: the drm device to register.
> + */
> +void drm_log_register(struct drm_device *dev)
> +{
> +	struct drm_log *new;
> +
> +	new = kzalloc(sizeof(*new), GFP_KERNEL);
> +	if (!new)
> +		goto err_warn;
> +
> +	mutex_init(&new->lock);
> +	if (drm_client_init(dev, &new->client, "drm_log", &drm_log_client_funcs))
> +		goto err_free;
> +
> +	drm_client_register(&new->client);
> +
> +	drm_log_register_console(&new->con);
> +
> +	drm_dbg(dev, "Registered with drm log as %s\n", new->con.name);
> +	return;
> +
> +err_free:
> +	kfree(new);
> +err_warn:
> +	drm_warn(dev, "Failed to register with drm log\n");
> +}

Dan Carpenter Dec. 12, 2024, 7:41 a.m. UTC | #2

This patch breaks "make oldconfig" for me.  It just gets into an endless
loop of:

  Default DRM Client
  choice[1-0?]: 0
  Default DRM Client
  choice[1-0?]: 0
  Default DRM Client
  choice[1-0?]: 0
  Default DRM Client
  choice[1-0?]: 0
  ...

I don't have to type anything, it just spams that forever.  It's weird
that it's 1-0 instead of 0-1.  Does that means something?  I don't know
much about Kconfig.

I'm using this arm64 randconfig as a base.  I type "make oldconfig" and
press enter until it gets to "Default DRM Client" and then it starts
scrolling endlessly.
https://download.01.org/0day-ci/archive/20241212/[e-mail]/config

regards,
dan carpenter

Jocelyn Falempe Dec. 12, 2024, 8:49 a.m. UTC | #3

On 12/12/2024 08:41, Dan Carpenter wrote:
> This patch breaks "make oldconfig" for me.  It just gets into an endless
> loop of:
> 
>    Default DRM Client
>    choice[1-0?]: 0
>    Default DRM Client
>    choice[1-0?]: 0
>    Default DRM Client
>    choice[1-0?]: 0
>    Default DRM Client
>    choice[1-0?]: 0
>    ...
> 
> I don't have to type anything, it just spams that forever.  It's weird
> that it's 1-0 instead of 0-1.  Does that means something?  I don't know
> much about Kconfig.

I can reproduce it with your provided config.

It looks like it happens if DRM_CLIENT_SELECTION is enabled, but none of 
the client is.
The attached patch should fix it, can you try it ?

I will submit that shortly.

Thanks for reporting it.

Best regards,

Dan Carpenter Dec. 12, 2024, 8:53 a.m. UTC | #4

On Thu, Dec 12, 2024 at 09:49:19AM +0100, Jocelyn Falempe wrote:
> On 12/12/2024 08:41, Dan Carpenter wrote:
> > This patch breaks "make oldconfig" for me.  It just gets into an endless
> > loop of:
> > 
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    ...
> > 
> > I don't have to type anything, it just spams that forever.  It's weird
> > that it's 1-0 instead of 0-1.  Does that means something?  I don't know
> > much about Kconfig.
> 
> I can reproduce it with your provided config.
> 
> It looks like it happens if DRM_CLIENT_SELECTION is enabled, but none of the
> client is.
> The attached patch should fix it, can you try it ?
> 

Thanks!

Tested-by: Dan Carpenter <[e-mail]>

regards,
dan carpenter

Simona Vetter Dec. 12, 2024, 10:07 a.m. UTC | #5

On Thu, Dec 12, 2024 at 09:49:19AM +0100, Jocelyn Falempe wrote:
> On 12/12/2024 08:41, Dan Carpenter wrote:
> > This patch breaks "make oldconfig" for me.  It just gets into an endless
> > loop of:
> > 
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    Default DRM Client
> >    choice[1-0?]: 0
> >    ...
> > 
> > I don't have to type anything, it just spams that forever.  It's weird
> > that it's 1-0 instead of 0-1.  Does that means something?  I don't know
> > much about Kconfig.
> 
> I can reproduce it with your provided config.
> 
> It looks like it happens if DRM_CLIENT_SELECTION is enabled, but none of the
> client is.
> The attached patch should fix it, can you try it ?
> 
> I will submit that shortly.
> 
> Thanks for reporting it.
> 
> Best regards,
> 
> -- 
> 
> Jocelyn
> 
> 
> > 
> > I'm using this arm64 randconfig as a base.  I type "make oldconfig" and
> > press enter until it gets to "Default DRM Client" and then it starts
> > scrolling endlessly.
> > https://download.01.org/0day-ci/archive/20241212/[e-mail]/config
> > 
> > regards,
> > dan carpenter
> > 

> From e4d197debd2c199c9f2d8e35e41e36c2836926b9 Mon Sep 17 00:00:00 2001
> From: Jocelyn Falempe <[e-mail]>
> Date: Thu, 12 Dec 2024 09:43:50 +0100
> Subject: [PATCH] Fix endless Kconfig loop
> 
> Signed-off-by: Jocelyn Falempe <[e-mail]>

Since I haven't seen the patch anywhere else I'll drop my ack here.

Acked-by: Simona Vetter <[e-mail]>

Please push directly to drm-misc-next so the breakage doesn't linger.
-Sima
> ---
>  drivers/gpu/drm/clients/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/clients/Kconfig b/drivers/gpu/drm/clients/Kconfig
> index c18decc90200..82a7d4e584dd 100644
> --- a/drivers/gpu/drm/clients/Kconfig
> +++ b/drivers/gpu/drm/clients/Kconfig
> @@ -87,6 +87,7 @@ config DRM_CLIENT_LOG
>  choice
>  	prompt "Default DRM Client"
>  	depends on DRM_CLIENT_SELECTION
> +	depends on DRM_FBDEV_EMULATION || DRM_CLIENT_LOG
>  	default DRM_CLIENT_DEFAULT_FBDEV
>  	help
>  	  Selects the default drm client.
> -- 
> 2.47.1
>

Markus Elfring Dec. 18, 2024, 12:25 p.m. UTC | #6

…
> +++ b/drivers/gpu/drm/clients/drm_log.c
> @@ -0,0 +1,370 @@
…
> +static int drm_log_count_modeset(struct drm_client_dev *client)
> +{
> +	struct drm_mode_set *mode_set;
> +	int count = 0;
> +
> +	mutex_lock(&client->modeset_mutex);
> +	drm_client_for_each_modeset(mode_set, client)
> +		count++;
> +	mutex_unlock(&client->modeset_mutex);
> +	return count;
> +}
…

Under which circumstances would you become interested to apply a statement
like “guard(mutex)(&client->modeset_mutex);”?
https://elixir.bootlin.com/linux/v6.13-rc3/source/include/linux/mutex.h#L201

Regards,
Markus

Jocelyn Falempe Dec. 18, 2024, 1:51 p.m. UTC | #7

On 18/12/2024 13:25, Markus Elfring wrote:
> …
>> +++ b/drivers/gpu/drm/clients/drm_log.c
>> @@ -0,0 +1,370 @@
> …
>> +static int drm_log_count_modeset(struct drm_client_dev *client)
>> +{
>> +	struct drm_mode_set *mode_set;
>> +	int count = 0;
>> +
>> +	mutex_lock(&client->modeset_mutex);
>> +	drm_client_for_each_modeset(mode_set, client)
>> +		count++;
>> +	mutex_unlock(&client->modeset_mutex);
>> +	return count;
>> +}
> …
> 
> Under which circumstances would you become interested to apply a statement
> like “guard(mutex)(&client->modeset_mutex);”?
> https://elixir.bootlin.com/linux/v6.13-rc3/source/include/linux/mutex.h#L201

Ok, I didn't know about this new syntax, thanks for pointing this to me.
Regarding drm_log, I kept the mutex usage simple, as there is only one 
mutex_lock() and one mutex_unlock() in each function, which means there 
is not much benefit to use the guard syntax.
I will keep that in mind, and if there is a need to have more complex 
mutex handling, I will probably use this.

Best regards,

Patch

diff --git a/drivers/gpu/drm/clients/Kconfig b/drivers/gpu/drm/clients/Kconfig
index 01ad3b000130..c18decc90200 100644
--- a/drivers/gpu/drm/clients/Kconfig
+++ b/drivers/gpu/drm/clients/Kconfig
@@ -12,6 +12,7 @@  config DRM_CLIENT_LIB
 config DRM_CLIENT_SELECTION
 	tristate
 	depends on DRM
+	select DRM_CLIENT_LIB if DRM_CLIENT_LOG
 	select DRM_CLIENT_LIB if DRM_FBDEV_EMULATION
 	help
 	  Drivers that support in-kernel DRM clients have to select this
@@ -70,4 +71,51 @@  config DRM_FBDEV_LEAK_PHYS_SMEM
 	  If in doubt, say "N" or spread the word to your closed source
 	  library vendor.
 
+config DRM_CLIENT_LOG
+	bool "Print the kernel boot message on the screen"
+	depends on DRM_CLIENT_SELECTION
+	select DRM_CLIENT
+	select DRM_CLIENT_SETUP
+	select DRM_DRAW
+	help
+	  This enable a drm logger, that will print the kernel messages to the
+	  screen until the userspace is ready to take over.
+
+	  If you only need logs, but no terminal, or if you prefer userspace
+	  terminal, say "Y".
+
+choice
+	prompt "Default DRM Client"
+	depends on DRM_CLIENT_SELECTION
+	default DRM_CLIENT_DEFAULT_FBDEV
+	help
+	  Selects the default drm client.
+
+	  The selection made here can be overridden by using the kernel
+	  command line 'drm_client_lib.active=fbdev' option.
+
+config DRM_CLIENT_DEFAULT_FBDEV
+	bool "fbdev"
+	depends on DRM_FBDEV_EMULATION
+	help
+	  Use fbdev emulation as default drm client. This is needed to have
+	  fbcon on top of a drm driver.
+
+config DRM_CLIENT_DEFAULT_LOG
+	bool "log"
+	depends on DRM_CLIENT_LOG
+	help
+	  Use drm log as default drm client. This will display boot logs on the
+	  screen, but doesn't implement a full terminal. For that you will need
+	  a userspace terminal using drm/kms.
+
+endchoice
+
+config DRM_CLIENT_DEFAULT
+       string
+       depends on DRM_CLIENT
+       default "fbdev" if DRM_CLIENT_DEFAULT_FBDEV
+       default "log" if DRM_CLIENT_DEFAULT_LOG
+       default ""
+
 endmenu
diff --git a/drivers/gpu/drm/clients/Makefile b/drivers/gpu/drm/clients/Makefile
index 1d004ec92e1e..c16addbc327f 100644
--- a/drivers/gpu/drm/clients/Makefile
+++ b/drivers/gpu/drm/clients/Makefile
@@ -1,5 +1,8 @@ 
 # SPDX-License-Identifier: GPL-2.0
 
+subdir-ccflags-y += -I$(src)/..
+
 drm_client_lib-y := drm_client_setup.o
+drm_client_lib-$(CONFIG_DRM_CLIENT_LOG) += drm_log.o
 drm_client_lib-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fbdev_client.o
 obj-$(CONFIG_DRM_CLIENT_LIB) += drm_client_lib.o
diff --git a/drivers/gpu/drm/clients/drm_client_internal.h b/drivers/gpu/drm/clients/drm_client_internal.h
index 23258934956a..6dc078bf6503 100644
--- a/drivers/gpu/drm/clients/drm_client_internal.h
+++ b/drivers/gpu/drm/clients/drm_client_internal.h
@@ -16,4 +16,10 @@  static inline int drm_fbdev_client_setup(struct drm_device *dev,
 }
 #endif
 
+#ifdef CONFIG_DRM_CLIENT_LOG
+void drm_log_register(struct drm_device *dev);
+#else
+static inline void drm_log_register(struct drm_device *dev) {}
+#endif
+
 #endif
diff --git a/drivers/gpu/drm/clients/drm_client_setup.c b/drivers/gpu/drm/clients/drm_client_setup.c
index 4b211a4812b5..e17265039ca8 100644
--- a/drivers/gpu/drm/clients/drm_client_setup.c
+++ b/drivers/gpu/drm/clients/drm_client_setup.c
@@ -7,6 +7,12 @@ 
 
 #include "drm_client_internal.h"
 
+static char drm_client_default[16] = CONFIG_DRM_CLIENT_DEFAULT;
+module_param_string(active, drm_client_default, sizeof(drm_client_default), 0444);
+MODULE_PARM_DESC(active,
+		 "Choose which drm client to start, default is"
+		 CONFIG_DRM_CLIENT_DEFAULT "]");
+
 /**
  * drm_client_setup() - Setup in-kernel DRM clients
  * @dev: DRM device
@@ -25,11 +31,26 @@ 
  */
 void drm_client_setup(struct drm_device *dev, const struct drm_format_info *format)
 {
-	int ret;
 
-	ret = drm_fbdev_client_setup(dev, format);
-	if (ret)
-		drm_warn(dev, "Failed to set up DRM client; error %d\n", ret);
+#ifdef CONFIG_DRM_FBDEV_EMULATION
+	if (!strcmp(drm_client_default, "fbdev")) {
+		int ret;
+
+		ret = drm_fbdev_client_setup(dev, format);
+		if (ret)
+			drm_warn(dev, "Failed to set up DRM client; error %d\n", ret);
+		return;
+	}
+#endif
+
+#ifdef CONFIG_DRM_CLIENT_LOG
+	if (!strcmp(drm_client_default, "log")) {
+		drm_log_register(dev);
+		return;
+	}
+#endif
+	if (strcmp(drm_client_default, ""))
+		drm_warn(dev, "Unknown DRM client %s\n", drm_client_default);
 }
 EXPORT_SYMBOL(drm_client_setup);
 
diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
new file mode 100644
index 000000000000..4e07bff6c864
--- /dev/null
+++ b/drivers/gpu/drm/clients/drm_log.c
@@ -0,0 +1,370 @@ 
+// SPDX-License-Identifier: GPL-2.0 or MIT
+/*
+ * Copyright (c) 2024 Red Hat.
+ * Author: Jocelyn Falempe <[e-mail]>
+ */
+
+#include <linux/console.h>
+#include <linux/font.h>
+#include <linux/init.h>
+#include <linux/iosys-map.h>
+#include <linux/module.h>
+#include <linux/types.h>
+
+#include <drm/drm_client.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_fourcc.h>
+#include <drm/drm_framebuffer.h>
+#include <drm/drm_print.h>
+
+#include "drm_client_internal.h"
+#include "drm_draw_internal.h"
+
+MODULE_AUTHOR("Jocelyn Falempe");
+MODULE_DESCRIPTION("DRM boot logger");
+MODULE_LICENSE("GPL");
+
+/**
+ * DOC: overview
+ *
+ * This is a simple graphic logger, to print the kernel message on screen, until
+ * a userspace application is able to take over.
+ * It is only for debugging purpose.
+ */
+
+struct drm_log_scanout {
+	struct drm_client_buffer *buffer;
+	const struct font_desc *font;
+	u32 rows;
+	u32 columns;
+	u32 line;
+	u32 format;
+	u32 px_width;
+	u32 front_color;
+};
+
+struct drm_log {
+	struct mutex lock;
+	struct drm_client_dev client;
+	struct console con;
+	bool probed;
+	u32 n_scanout;
+	struct drm_log_scanout *scanout;
+};
+
+static struct drm_log *client_to_drm_log(struct drm_client_dev *client)
+{
+	return container_of(client, struct drm_log, client);
+}
+
+static struct drm_log *console_to_drm_log(struct console *con)
+{
+	return container_of(con, struct drm_log, con);
+}
+
+static void drm_log_blit(struct iosys_map *dst, unsigned int dst_pitch,
+			 const u8 *src, unsigned int src_pitch,
+			 u32 height, u32 width, u32 scale, u32 px_width, u32 color)
+{
+	switch (px_width) {
+	case 2:
+		drm_draw_blit16(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		break;
+	case 3:
+		drm_draw_blit24(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		break;
+	case 4:
+		drm_draw_blit32(dst, dst_pitch, src, src_pitch, height, width, scale, color);
+		break;
+	default:
+		WARN_ONCE(1, "Can't blit with pixel width %d\n", px_width);
+	}
+}
+
+static void drm_log_clear_line(struct drm_log_scanout *scanout, u32 line)
+{
+	struct drm_framebuffer *fb = scanout->buffer->fb;
+	unsigned long height = scanout->font->height;
+	struct iosys_map map;
+	struct drm_rect r = DRM_RECT_INIT(0, line * height, fb->width, height);
+
+	if (drm_client_buffer_vmap_local(scanout->buffer, &map))
+		return;
+	iosys_map_memset(&map, r.y1 * fb->pitches[0], 0, height * fb->pitches[0]);
+	drm_client_buffer_vunmap_local(scanout->buffer);
+	drm_client_framebuffer_flush(scanout->buffer, &r);
+}
+
+static void drm_log_draw_line(struct drm_log_scanout *scanout, const char *s,
+			      unsigned int len)
+{
+	struct drm_framebuffer *fb = scanout->buffer->fb;
+	struct iosys_map map;
+	const struct font_desc *font = scanout->font;
+	size_t font_pitch = DIV_ROUND_UP(font->width, 8);
+	const u8 *src;
+	u32 px_width = fb->format->cpp[0];
+	struct drm_rect r = DRM_RECT_INIT(0, scanout->line * font->height,
+					  fb->width, (scanout->line + 1) * font->height);
+	u32 i;
+
+	if (drm_client_buffer_vmap_local(scanout->buffer, &map))
+		return;
+
+	iosys_map_incr(&map, r.y1 * fb->pitches[0]);
+	for (i = 0; i < len && i < scanout->columns; i++) {
+		src = drm_draw_get_char_bitmap(font, s[i], font_pitch);
+		drm_log_blit(&map, fb->pitches[0], src, font_pitch, font->height, font->width,
+			     1, px_width, scanout->front_color);
+		iosys_map_incr(&map, font->width * px_width);
+	}
+
+	scanout->line++;
+	if (scanout->line >= scanout->rows)
+		scanout->line = 0;
+	drm_client_buffer_vunmap_local(scanout->buffer);
+	drm_client_framebuffer_flush(scanout->buffer, &r);
+}
+
+static void drm_log_draw_new_line(struct drm_log_scanout *scanout,
+				  const char *s, unsigned int len)
+{
+	if (scanout->line == 0) {
+		drm_log_clear_line(scanout, 0);
+		drm_log_clear_line(scanout, 1);
+		drm_log_clear_line(scanout, 2);
+	} else if (scanout->line + 2 < scanout->rows)
+		drm_log_clear_line(scanout, scanout->line + 2);
+
+	drm_log_draw_line(scanout, s, len);
+}
+
+static void drm_log_draw_kmsg_record(struct drm_log_scanout *scanout,
+				     const char *s, unsigned int len)
+{
+	/* do not print the ending \n character */
+	if (s[len - 1] == '\n')
+		len--;
+
+	while (len > scanout->columns) {
+		drm_log_draw_new_line(scanout, s, scanout->columns);
+		s += scanout->columns;
+		len -= scanout->columns;
+	}
+	if (len)
+		drm_log_draw_new_line(scanout, s, len);
+}
+
+static u32 drm_log_find_usable_format(struct drm_plane *plane)
+{
+	int i;
+
+	for (i = 0; i < plane->format_count; i++)
+		if (drm_draw_color_from_xrgb8888(0xffffff, plane->format_types[i]) != 0)
+			return plane->format_types[i];
+	return DRM_FORMAT_INVALID;
+}
+
+static int drm_log_setup_modeset(struct drm_client_dev *client,
+				 struct drm_mode_set *mode_set,
+				 struct drm_log_scanout *scanout)
+{
+	struct drm_crtc *crtc = mode_set->crtc;
+	u32 width = mode_set->mode->hdisplay;
+	u32 height = mode_set->mode->vdisplay;
+	u32 format;
+
+	scanout->font = get_default_font(width, height, NULL, NULL);
+	if (!scanout->font)
+		return -ENOENT;
+
+	format = drm_log_find_usable_format(crtc->primary);
+	if (format == DRM_FORMAT_INVALID)
+		return -EINVAL;
+
+	scanout->buffer = drm_client_framebuffer_create(client, width, height, format);
+	if (IS_ERR(scanout->buffer)) {
+		drm_warn(client->dev, "drm_log can't create framebuffer %d %d %p4cc\n",
+			 width, height, &format);
+		return -ENOMEM;
+	}
+	mode_set->fb = scanout->buffer->fb;
+	scanout->rows = height / scanout->font->height;
+	scanout->columns = width / scanout->font->width;
+	scanout->front_color = drm_draw_color_from_xrgb8888(0xffffff, format);
+	return 0;
+}
+
+static int drm_log_count_modeset(struct drm_client_dev *client)
+{
+	struct drm_mode_set *mode_set;
+	int count = 0;
+
+	mutex_lock(&client->modeset_mutex);
+	drm_client_for_each_modeset(mode_set, client)
+		count++;
+	mutex_unlock(&client->modeset_mutex);
+	return count;
+}
+
+static void drm_log_init_client(struct drm_log *dlog)
+{
+	struct drm_client_dev *client = &dlog->client;
+	struct drm_mode_set *mode_set;
+	int i, max_modeset;
+	int n_modeset = 0;
+
+	dlog->probed = true;
+
+	if (drm_client_modeset_probe(client, 0, 0))
+		return;
+
+	max_modeset = drm_log_count_modeset(client);
+	if (!max_modeset)
+		return;
+
+	dlog->scanout = kcalloc(max_modeset, sizeof(*dlog->scanout), GFP_KERNEL);
+	if (!dlog->scanout)
+		return;
+
+	mutex_lock(&client->modeset_mutex);
+	drm_client_for_each_modeset(mode_set, client) {
+		if (!mode_set->mode)
+			continue;
+		if (drm_log_setup_modeset(client, mode_set, &dlog->scanout[n_modeset]))
+			continue;
+		n_modeset++;
+	}
+	mutex_unlock(&client->modeset_mutex);
+	if (n_modeset == 0)
+		goto err_nomodeset;
+
+	if (drm_client_modeset_commit(client))
+		goto err_failed_commit;
+
+	dlog->n_scanout = n_modeset;
+	return;
+
+err_failed_commit:
+	for (i = 0; i < n_modeset; i++)
+		drm_client_framebuffer_delete(dlog->scanout[i].buffer);
+
+err_nomodeset:
+	kfree(dlog->scanout);
+	dlog->scanout = NULL;
+}
+
+static void drm_log_free_scanout(struct drm_client_dev *client)
+{
+	struct drm_log *dlog = client_to_drm_log(client);
+	int i;
+
+	if (dlog->n_scanout) {
+		for (i = 0; i < dlog->n_scanout; i++)
+			drm_client_framebuffer_delete(dlog->scanout[i].buffer);
+		dlog->n_scanout = 0;
+		kfree(dlog->scanout);
+		dlog->scanout = NULL;
+	}
+}
+
+static void drm_log_client_unregister(struct drm_client_dev *client)
+{
+	struct drm_log *dlog = client_to_drm_log(client);
+	struct drm_device *dev = client->dev;
+
+	unregister_console(&dlog->con);
+
+	mutex_lock(&dlog->lock);
+	drm_log_free_scanout(client);
+	drm_client_release(client);
+	mutex_unlock(&dlog->lock);
+	kfree(dlog);
+	drm_dbg(dev, "Unregistered with drm log\n");
+}
+
+static int drm_log_client_hotplug(struct drm_client_dev *client)
+{
+	struct drm_log *dlog = client_to_drm_log(client);
+
+	mutex_lock(&dlog->lock);
+	drm_log_free_scanout(client);
+	dlog->probed = false;
+	mutex_unlock(&dlog->lock);
+	return 0;
+}
+
+static const struct drm_client_funcs drm_log_client_funcs = {
+	.owner		= THIS_MODULE,
+	.unregister	= drm_log_client_unregister,
+	.hotplug	= drm_log_client_hotplug,
+};
+
+static void drm_log_write_thread(struct console *con, struct nbcon_write_context *wctxt)
+{
+	struct drm_log *dlog = console_to_drm_log(con);
+	int i;
+
+	if (!dlog->probed)
+		drm_log_init_client(dlog);
+
+	for (i = 0; i < dlog->n_scanout; i++)
+		drm_log_draw_kmsg_record(&dlog->scanout[i], wctxt->outbuf, wctxt->len);
+}
+
+static void drm_log_lock(struct console *con, unsigned long *flags)
+{
+	struct drm_log *dlog = console_to_drm_log(con);
+
+	mutex_lock(&dlog->lock);
+	migrate_disable();
+}
+
+static void drm_log_unlock(struct console *con, unsigned long flags)
+{
+	struct drm_log *dlog = console_to_drm_log(con);
+
+	migrate_enable();
+	mutex_unlock(&dlog->lock);
+}
+
+static void drm_log_register_console(struct console *con)
+{
+	strscpy(con->name, "drm_log");
+	con->write_thread = drm_log_write_thread;
+	con->device_lock = drm_log_lock;
+	con->device_unlock = drm_log_unlock;
+	con->flags = CON_PRINTBUFFER | CON_NBCON;
+	con->index = -1;
+
+	register_console(con);
+}
+
+/**
+ * drm_log_register() - Register a drm device to drm_log
+ * @dev: the drm device to register.
+ */
+void drm_log_register(struct drm_device *dev)
+{
+	struct drm_log *new;
+
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		goto err_warn;
+
+	mutex_init(&new->lock);
+	if (drm_client_init(dev, &new->client, "drm_log", &drm_log_client_funcs))
+		goto err_free;
+
+	drm_client_register(&new->client);
+
+	drm_log_register_console(&new->con);
+
+	drm_dbg(dev, "Registered with drm log as %s\n", new->con.name);
+	return;
+
+err_free:
+	kfree(new);
+err_warn:
+	drm_warn(dev, "Failed to register with drm log\n");
+}