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

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Message-ID: <xeipdyk2i2lpkg4rrvz4cl2l3ch62sl4zoa73qvlms3ek3zkci@y7xqbgjulaet>
Date: Wed, 17 Sep 2025 11:14:45 -0400
From: Nick Bowler <nbowler@...conx.ca>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: Doug Anderson <dianders@...omium.org>, 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)

On Fri, Aug 29, 2025 at 03:07:14PM +0200, Thomas Zimmermann wrote:
> it's been a while since you sent this report. I assume, the problem is this
> there?

Sorry, I haven't had much time to try the latest versions, the most
recent version tested is 6.15-rc7 and the problem occurs there.

I have just patched out the shutdown call in the ast driver and
everything is fine.

> Am 30.04.25 um 15:28 schrieb Nick Bowler:
> > On Mon, Apr 28, 2025 at 01:40:25PM -0700, Doug Anderson wrote:
[...]
> > > 2. Could you give more details about what panel you're using?
> > According to the documentation I have for the machine, the video output
> > of the AST2500 BMC is connected to an IT66121 HDMI transmitter.
> 
> That dmesg refers to a SIL164. I always thought these where only for DVI.
> With the IT66121, I'd expect the warning from [1] in the dmesg.

It's not impossible that there is an error in the documentation.

Although the comment in the driver right above the linked code suggests
that it might just report SIL164 even for other kinds of transmitter
chips?

> [1] https://elixir.bootlin.com/linux/v6.16.3/source/drivers/gpu/drm/ast/ast_main.c#L196
> 
> 
> The ast driver doesn't do much during shutdown. Could you please out-comment
> the lines at either [2] xor [3] and report on either effect? These calls
> turn of the video chip's memory access and sync pulses. Not doing that might
> resolve the problem.
> 
> [2] https://elixir.bootlin.com/linux/v6.16.3/source/drivers/gpu/drm/ast/ast_mode.c#L835
> [3] https://elixir.bootlin.com/linux/v6.16.3/source/drivers/gpu/drm/ast/ast_mode.c#L839

I can try this.

Thanks,
  Nick