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

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Message-ID: <2d62f7a1-712f-4868-8e21-e2d5b616c43a@suse.de>
Date: Thu, 18 Sep 2025 12:46:04 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Nick Bowler <nbowler@...conx.ca>
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)

Hi

Am 18.09.25 um 04:04 schrieb Nick Bowler:
> On Wed, Sep 17, 2025 at 11:14:45AM -0400, Nick Bowler wrote:
>> On Fri, Aug 29, 2025 at 03:07:14PM +0200, Thomas Zimmermann wrote:
>>> 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.
> OK, I tested 6.17-rc6 and reproduced the problem on this version.  Then:
>
>    - Deleting [2] (only) appears to make no difference whatsoever. That
>      is, deleting the following line in ast_mode.c:
>
>        ast_set_index_reg_mask(ast, AST_IO_VGASRI, 0x01, 0xdf, AST_IO_VGASR1_SD);
>
>    - Deleting [3] (only) appears sufficient to make things work again,
>      that is, deleting the following line in ast_mode.c:
>
>        ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xb6, 0xfc, vgacrb6);

Great, thanks for testing! I'll see if i can make a workaround for your 
system.

Could you please provide me with 'lspci -nvv' of the device?

Best regards
Thomas

>
> Thanks,
>    Nick

-- 
--
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)