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SubjectRe: [PATCH] ARM: early_printk: respect keep parameter
On Tue, 17 Jul 2018, Alexandre Belloni wrote:

> 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@bootlin.com>
> >
> > 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

That is a good analysis, but not necessarily a good argument for this
particular patch.

> > 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.

Yes, that certainly fits. This is not what your commit log message is
saying though.

> Also, atmel_serial doesn't yet have earlycon support.

Fair enough, and probably something you should mention too.

> > > ---
> > > 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
>

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