Re: [PATCH] arch: arm64: dts: apple: Remove stdout-path

[Akihiko Odaki]

On 2022/12/02 2:46, Hector Martin wrote:
> On 02/12/2022 01.38, Akihiko Odaki wrote:
> >   >> In contrary, if you boot the kernel without the hypervisor
> >   >> feature and this change, you will completely lose the console.
> >   >
> >   > How so? The console goes to both places with stdout-path set to serial0.
> >   > What it *does* change is where input is accepted prior to getty startup
> >   > (which is why u-boot specifically conditions this on keyboard presence,
> >   > modulo the USB issue - because if you *don't* have a keyboard then tty
> >   > keyboard input is useless). But if you're booting kernels without u-boot
> >   > along the way, you're probably doing it from the hypervisor or linux.py
> >   > anyway, especially if you plan to do something like "init=/bin/sh",
> >   > because without u-boot (+ optionally some EFI loader) there is no way of
> >   > editing command line arguments at boot time stand-alone.
> >
> > Well, that is not exactly the behavior I saw. In my case, if stdout-path
> > is pointed to serial, there is no output on the framebuffer, and it just
> > printed "_".
> >
> > It looks like the kernel only outputs to either of serial and
> > framebuffer, not both.
>
> That is not what I've seen in all of my hypervisor runs since the dawn
> of time. You get log output on both.
>
> > What I experienced is that when I directly booted the kernel from m1n1
> > without hypervisor, it showed no output to the display even though the
> > same kernel worked with U-Boot. While I could tell it used wrong console
> > by running the hypervisor, I wondered why it behaves differently without
> > U-Boot, and found the aforementioned U-Boot change, coming up with this
> > patch.
>
> Then it sounds like something else is different about our setups,
> because I've booted the kernel from linux.py hundreds of times and I get
> output on both. Looking through the console code, the VT console gets
> added and enabled really early, and the subsequent serial console
> registration later does not disable it.
>
> Look for "console: colour dummy device 80x25". It should be immediately
> followed by "printk: console [tty0] enabled", and this should all come
> well before the ttySAC0 serial stuff shows up.
>
> - Hector

I think I understand the situation now. By "console", I was meaning the 
input and output of init, but I failed to clarify that and you thought 
it referring to kernel message output. I saw no messages earlier than 
init because my kernel command line has loglevel=3.

Regards,
Akihiko Odaki