PROBLEM: AST2500 BMC video output disabled by reboot (regression)

[Nick Bowler]

Hi,

On Wed, Apr 30, 2025 at 10:05:44AM -0700, Doug Anderson wrote:
> On Wed, Apr 30, 2025 at 6:28 AM Nick Bowler <nbowler at draconx.ca> wrote:
> > On Mon, Apr 28, 2025 at 01:40:25PM -0700, Doug Anderson wrote:
> > > On Sun, Apr 20, 2025 at 9:26 PM Nick Bowler <nbowler at draconx.ca> wrote:
> > > > I recently noticed that on current kernels I lose video output from
> > > > my Blackbird's AST2500 BMC after a reboot
> > [...]
> > > >   ce3d99c8349584bc0fbe1e21918a3ea1155343aa is the first bad commit
> > > >   commit ce3d99c8349584bc0fbe1e21918a3ea1155343aa
> > > >   Author: Douglas Anderson <dianders at chromium.org>
> > > >   Date:   Fri Sep 1 16:39:53 2023 -0700
> > > >
> > > >       drm: Call drm_atomic_helper_shutdown() at shutdown time for misc drivers
[...]
> Do you happen to have anything that's just a normal HDMI sink, like a
> TV or a standard monitor that takes HDMI?

I can probably find something else to try later.

> > 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.

> I guess I'd be interested in other types of tests to see what's going
> on. Aside from trying some other, more standard HDMI sinks, I'd love
> to see the results of:
> 
> 1. HDMI is supposed to be hotpluggable. If you've got a boot where the
> display isn't working, what if you unplug the HDMI and plug it back
> in. Does it fix it?

Unplugging/replugging the cable when the video is off after rebooting
does not cause it to start working again.

> 2. Does the hotplug experience change if you boot with the revert?
> AKA: boot up with the revert (so everything is working normally),
> unplug HDMI, wait a few seconds, plug HDMI back in? Is this different
> than #1?

I have certainly never noticed any problem related to hot plugging while
the video output is working but this is not something I ever normally
do.  I can try it later.

> 3. What about if you fully power off and then power on? Does the
> display work reliably in this case, or are things different between
> ToT and with the revert?

There is never any problem with the video output if I fully power off/on
the system.  The problem only occurs on a reboot.

> 4. What about if you fully power off, unplug the HDMI, wait a few
> seconds, plug the HDMI, and power on? Does that work? Are things
> different between ToT and with the revert?

Again there is never any problem if I fully power off/on the system.

Thanks,
  Nick