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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMuHMdXQ1N2N5WBfG3KeC1fPz+ez+fzDriKm8omHxfhe6m_Pfg@mail.gmail.com>
Date: Wed, 18 Dec 2024 16:03:04 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Jocelyn Falempe <jfalempe@...hat.com>
Cc: Petr Mladek <pmladek@...e.com>, 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>, 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 18, 2024 at 3:58 PM Jocelyn Falempe <jfalempe@...hat.com> wrote:
> On 18/12/2024 15:18, Petr Mladek wrote:
> > On Wed 2024-12-18 12:41:39, Jocelyn Falempe wrote:
> >> On 18/12/2024 12:00, Geert Uytterhoeven wrote:
> >>> On Wed, Dec 18, 2024 at 11:14 AM Jocelyn Falempe <jfalempe@...hat.com> wrote:
> >>>> Maybe you need to add console=drm_log to your kernel command line, so
> >>>> the kernel will actually use this console.
> >>>
> >>> Thanks, that does the trick!
> >>>
> >>> Note that I do not need to specify any console= kernel command line
> >>> parameter for the fbdev console.
> >>
> >> Yes, the fbcon console is tty0, which is hardcoded for historical reason.
> >> Some architectures use add_preferred_console() to enable specific consoles,
> >> I'm not sure it's allowed to use that from the drm_log_register() code.
> >
> > add_preferred_console() is used when the console should get enabled
> > intentionally. I would split the intentions into two categories:
> >
> >    + requested by the end-user on the command line, see
> >         __add_preferred_console(..., true) in console_setup()
> >
> >    + enabled by default by a hardware definition (manufacture), see
> >         add_preferred_console() in:
> >
> >       + of_console_check(): generic solution via device tree
> >       + acpi_parse_spcr(): generic solution via SPCR table
> >       + *: hardcoded in few more HW-specific drivers
> >
> > add_preferred_console() causes the console will always get enabled
> > when it is successfully initialized.
> >
> > So, should the "drm_log" console get always enabled?
>
> drm_log is a replacement for fbcon, which is always enabled, so I think
> it should also be always enabled. Otherwise you won't get any console as
> fbcon is no more available.
> drm_log doesn't really fit in the architecture/hardware model, because
> drm drivers are available for a wide range of architecture, and a GPU
> can do either fbdev/fbcon or drm_log.
>
> >> I will still send a patch to add update the Kconfig help for drm_log, as
> >> this command line argument is required to have it working.
> >
> > I guess that the drm_log consoles should get enabled only when
> > requested by the user => documenting the command line parameter
> > is the right solution here.
>
> Most embedded linux specify the console on the command line, but for
> laptop/desktop distributions, it's not the case as fbcon is the default
> since the beginning.

Note that on embedded systems with DT, the console is auto-selected
via chosen/stdout-path. No explicit console= needed.

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