linux-kernel - Re: PROBLEM: AST2500 BMC video output disabled by reboot (regression)

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Message-ID: <CAD=FV=U4PdTgRsxJ3HVRRQEZAPHinKxhUE9FpKDOnv=nDQo3KQ@mail.gmail.com>
Date: Wed, 30 Apr 2025 16:31:02 -0700
From: Doug Anderson <dianders@...omium.org>
To: Nick Bowler <nbowler@...conx.ca>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	regressions@...ts.linux.dev
Subject: Re: PROBLEM: AST2500 BMC video output disabled by reboot (regression)

Hi,

On Wed, Apr 30, 2025 at 10:52 AM Nick Bowler <nbowler@...conx.ca> wrote:
>
> > > To clarify, there is no boot failure.  There is just no video output
> > > after rebooting.  I can then boot Linux again by any method that works
> > > without being able to see the screen, and then everything is fine once
> > > I do that.
> >
> > Super weird. So every other boot works?
>
> On a new/broken kernel, every time I run "reboot" the video turns off
> when Linux does whatever it does to make the system restart.
>
> The video comes on again if I manage to boot it up again.
>
> The problem is that I have to do that without using the screen.  So I
> can boot Linux via the serial port, or via the BMC web interface, or
> by just typing on the keyboard without seeing what is happening.

Ohhhhhh! I was assuming that your problem looked like this:

1. Boot up Linux, video works.

2. Type "reboot" and the system boots back to Linux w/ no video.

3. Log into Linux via UART or ssh and type "reboot". System boots back
to Linux and video works.

...and then if you repeat steps #2 and #3 it keeps alternating with
Linux having video and not having video.

It sounds like instead what you're saying is that you're typing
"reboot" and then booting into some other operating system / BIOS and
the video doesn't work in that other (non-Linux) environment. Is that
right?

If I (finally) got it right, then I'm not really sure what to suggest.
It would sure seem like a bug in the other OS/BIOS. We could possibly
land the revert you have. I'd imagine it's papering over the bug, but
it's no real skin off my teeth. As a test, I'd imagine that if you
turned the screen off via commandline (I never really do this, but a
search turns up [1]) and then reboot with the screen off then I'd
imagine you run into the same trouble with or without the patch. Is
that true?

FWIW: The original incentive for adding all the shutdown calls (aside
from the fact that it's documented that they should be there) was to
make sure embedded panels shutdown properly. It looks as if no
embedded panels will really be used with this driver anyway.

[1] https://www.baeldung.com/linux/cli-monitor-turn-on-off