Hi Jocelyn,
On Wed, Dec 18, 2024 at 3:58 PM Jocelyn Falempe <jfalempe@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx
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
