Re: [PATCH] ARM: early_printk: respect keep parameter

From: Alexandre Belloni
Date: Tue Jul 17 2018 - 16:31:58 EST


On 17/07/2018 16:16:44-0400, Nicolas Pitre wrote:
> On Wed, 11 Jul 2018, Alexandre Belloni wrote:
>
> > Parse and use the keep parameter of earlyprintk to avoid having the kernel
> > output stop with:
> >
> > Console: colour dummy device 80x30
> > console [tty0] enabled
> > bootconsole [earlycon0] disabled
> >
> > This happens because once tty0, the virtual terminal console is registered,
> > it is selected as the default console, disregarding an existing stdout-path
> > DT property and the early console is shutdown before the console driver is
> > probed.
> >
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
>
> Why can't you have a real console driver that takes over at that point
> which respects whatever DT property you give it?
>

See Russell's analysis here:

https://www.spinics.net/lists/linux-serial/msg25363.html


> The early_printk code is very raw and inefficient, and it shouldn't be
> used for anything but the debugging of early boot hangs.
>

The issue I had is that he pinctrl driver wasn't probing so the real
console driver could never probe. I think this fits the use case.

Also, atmel_serial doesn't yet have earlycon support.

> > ---
> > arch/arm/kernel/early_printk.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/arm/kernel/early_printk.c b/arch/arm/kernel/early_printk.c
> > index 9257736ec9fa..bbb10150b11a 100644
> > --- a/arch/arm/kernel/early_printk.c
> > +++ b/arch/arm/kernel/early_printk.c
> > @@ -42,6 +42,9 @@ static struct console early_console_dev = {
> >
> > static int __init setup_early_printk(char *buf)
> > {
> > + if (buf && strstr(buf, "keep"))
> > + early_console_dev.flags &= ~CON_BOOT;
> > +
> > early_console = &early_console_dev;
> > register_console(&early_console_dev);
> > return 0;
> > --
> > 2.18.0
> >
> >
>

--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com