linux-kernel - Re: [PATCH v9 0/6] drm/log: Introduce a new boot logger to draw the kmsg on the screen

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Message-ID: <ca4485de-5463-4356-a024-fcabde45478d@redhat.com>
Date: Tue, 10 Dec 2024 14:42:39 +0100
From: Jocelyn Falempe <jfalempe@...hat.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 John Ogness <john.ogness@...utronix.de>,
 Javier Martinez Canillas <javierm@...hat.com>,
 "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
 bluescreen_avenger@...izon.net, Caleb Connolly <caleb.connolly@...aro.org>,
 Petr Mladek <pmladek@...e.com>, Jani Nikula <jani.nikula@...ux.intel.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 0/6] drm/log: Introduce a new boot logger to draw the
 kmsg on the screen

On 04/12/2024 16:44, Jocelyn Falempe wrote:
> 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.
> 
> If you're curious on how it looks like, I've put a small demo here:
> https://people.redhat.com/jfalempe/drm_log/drm_log_draft_boot_v2.mp4

I just pushed it to drm-misc-next.

Thanks all for your reviews and comments.

Best regards,

-- 

Jocelyn
> 
> 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
>   
> 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.
>   * Add suspend/resume callbacks.
>   * Add integer scaling support.
>   
> v5:
>   * Build drm_log in drm_client_lib module, to avoid circular dependency.
>   * Export drm_draw symbols, so they can be used if drm_client_lib is built as module.
>   * Change scale parameter to unsigned int (Jani Nikula)
> 
> v6:
>   * Use console_stop() and console_start() in the suspend/resume callback (Petr Mladek).
>   * rebase and solve conflict with "drm/panic: Add ABGR2101010 support"
> 
> v7:
>   * Add a patch fix a build issue due to missing DRM_CLIENT_LIB, reported by kernel test bot.
> 
> v8:
>   * Rebased after drm client moved to drivers/gpu/drm/clients/
>   * Rename DRM_LOG to DRM_CLIENT_LOG (Thomas Zimmermann)
>   * Drop "Always select DRM_CLIENT_LIB", and select only if DRM_CLIENT_LOG is set
>   * Add an info message if no clients are initialized in drm_client_setup()
> 
> v9:
>   * Rename drm_draw.h to drm_draw_internal.h (Jani Nikula)
>   * 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)
>   
> Jocelyn Falempe (6):
>    drm/panic: Move drawing functions to drm_draw
>    drm/log: Introduce a new boot logger to draw the kmsg on the screen
>    drm/log: Do not draw if drm_master is taken
>    drm/log: Color the timestamp, to improve readability
>    drm/log: Implement suspend/resume
>    drm/log: Add integer scaling support
> 
>   drivers/gpu/drm/Kconfig                       |   5 +
>   drivers/gpu/drm/Makefile                      |   1 +
>   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             | 420 ++++++++++++++++++
>   drivers/gpu/drm/drm_draw.c                    | 233 ++++++++++
>   drivers/gpu/drm/drm_draw_internal.h           |  56 +++
>   drivers/gpu/drm/drm_panic.c                   | 257 +----------
>   10 files changed, 820 insertions(+), 238 deletions(-)
>   create mode 100644 drivers/gpu/drm/clients/drm_log.c
>   create mode 100644 drivers/gpu/drm/drm_draw.c
>   create mode 100644 drivers/gpu/drm/drm_draw_internal.h
> 
> 
> base-commit: c6eabbab359c156669e10d5dec3e71e80ff09bd2