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: <CAMuHMdU925NiJDy4fOcQhA=jp8=79rZ3h5-TYxCjzkGwqQdKOg@mail.gmail.com>
Date: Tue, 17 Dec 2024 15:19:52 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Jocelyn Falempe <jfalempe@...hat.com>
Cc: 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, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v9 0/6] drm/log: Introduce a new boot logger to draw the
 kmsg on the screen

Hi Jocelyn,

On Wed, Dec 4, 2024 at 6:41 PM Jocelyn Falempe <jfalempe@...hat.com> 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
>
> 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

I gave this a try on Koelsch (R-Car M2-W), using rcar-du.
Unfortunately I don't see any kernel messages, and my monitor complains
about no signal. Does this require special support from the driver?

    CONFIG_DRM_CLIENT=y
    CONFIG_DRM_CLIENT_LIB=y
    CONFIG_DRM_CLIENT_SELECTION=y
    CONFIG_DRM_CLIENT_SETUP=y
    CONFIG_DRM_CLIENT_LOG=y
    # CONFIG_DRM_CLIENT_DEFAULT_FBDEV is not set
    CONFIG_DRM_CLIENT_DEFAULT_LOG=y
    CONFIG_DRM_CLIENT_DEFAULT="log"

Switching to fbdev gives a working display, as before:

    CONFIG_DRM_CLIENT_DEFAULT_FBDEV=y
    # CONFIG_DRM_CLIENT_DEFAULT_LOG is not set
    CONFIG_DRM_CLIENT_DEFAULT="fbdev"

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds