linux-kernel - Re: [REGRESSION][BISECTED] Screen goes blank with ASpeed AST2300 in 6.18-rc2

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Message-ID: <43992c88-3a3a-4855-9f46-27a7e5fdec2e@suse.de>
Date: Wed, 22 Oct 2025 08:51:30 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Peter Schneider <pschneider1968@...glemail.com>,
 regressions@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>
Cc: dri-devel@...ts.freedesktop.org, stable@...r.kernel.org,
 jfalempe@...hat.com, airlied@...hat.com, dianders@...omium.org,
 nbowler@...conx.ca, Linus Torvalds <torvalds@...ux-foundation.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [REGRESSION][BISECTED] Screen goes blank with ASpeed AST2300 in
 6.18-rc2

Hi

Am 22.10.25 um 05:27 schrieb Peter Schneider:
> #regzbot introduced: 6f719373b943a955fee6fc2012aed207b65e2854
>
> Hi all,
>
> I have encountered a serious (for me) regression with 6.18-rc2 on my 
> 2-socket Ivy Bridge Xeon E5-2697 v2 server. After booting, my console 
> screen goes blank and stays blank. 6.18-rc1 was still fine.
>
> The machine has an Asus Z9PE-D16 server mainboard with an onboard 
> ASpeed AST2300 VGA chip with 16MB VRAM. I have attached an older HP 
> Monitor to it via old VGA jack/cable. It also has a second graphics 
> card in a PCI-E slot; an older NVidia GTX 560. It is not connected to 
> a monitor, but I have configured it via kernel command line for 
> PCI-pass-through to VMs running on this server (I use Proxmox VE, i.e. 
> QEMU/KVM virtual machines). Currently, no VMs use this yet, and also 
> no VMs are autostarting with machine boot. So when this regression 
> occurs, the server is idle. Pressing a key on the keyboard does not 
> make the screen come alive. The server is running fine though, and I 
> can access it via SSH. It just has no graphic output anymore. In case 
> this is important, the machine also has a ASMB6 BMC (can be used via 
> http).
>
> I have attached dmesg output from both 6.18-rc1 which is fine, and 
> 6.18-rc2 which exhibits this bug. I have bisected the issue, please 
> see attached git bisect.log.

Thanks for the detailed bug report.

Attached is a patch that partially reverts the broken commit. Could you 
please apply it on top of the broken kernel and report on the results?

Best regards
Thomas

>
> The bad commit is
>
> commit 6f719373b943a955fee6fc2012aed207b65e2854
> Author: Thomas Zimmermann <tzimmermann@...e.de>
> Date:   Tue Oct 14 10:46:34 2025 +0200
>
>     drm/ast: Blank with VGACR17 sync enable, always clear VGACRB6 sync 
> off
>
>     Blank the display by disabling sync pulses with VGACR17<7>. Unblank
>     by reenabling them. This VGA setting should be supported by all 
> Aspeed
>     hardware.
>
> When I revert this from 6.18-rc2, the issue goes away and my console 
> screen works again.
>
> I just saw that Greg just yesterday evening included the offending 
> patch already in stable RCs 6.12.55-rc1 and 6.17.5-rc1, so I'll test 
> these seperately and send a mail to the stable mailing list, too, if 
> affected (which I anticipate).
>
> Beste Grüße,
> Peter Schneider
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)


View attachment "0001-ast-Set-clear-screen-disable-bit.patch" of type "text/x-patch" (1714 bytes)