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

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Message-ID: <5949fd73-3ca4-4bd9-8092-2d9923dcbfd3@suse.de>
Date: Wed, 1 Oct 2025 09:26:28 +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 Nick

Am 18.09.25 um 13:17 schrieb Thomas Zimmermann:
> 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);
>
> Please test if the attached patch fixes the problem for you.

Have you been able to test the patch?

Best regards
Thomas

>
> 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)