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

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Message-ID: <e0104f10-9230-41e5-acd1-4ca95c38220e@suse.de>
Date: Tue, 7 Oct 2025 10:51:29 +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 04.10.25 um 02:31 schrieb Nick Bowler:
> On Wed, Oct 01, 2025 at 09:26:28AM +0200, Thomas Zimmermann wrote:
>> Am 18.09.25 um 13:17 schrieb Thomas Zimmermann:
>>> 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?
> [...]
>>>>>> [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
> [...]
>>>>     - 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?
> In the normal scenario where everything is working and I reboot, then
> the display remains on for the firmware (this would seem to be an
> improvement).
>
> But it introduces a new problem: the screen no longer turns back on if
> I boot the patched kernel from the "display off" state.  The unpatched
> 6.17 kernel would at least turn the display back on from this.
> Furthermore, rebooting from this state keeps the display off.
>
> The earlier change [3] above has no such problems.

Thanks again for testing. Looks like your BMC is especially picky about 
these settings. :)

Attached are two patches; each trying to eliminate one of the possible 
causes. Could you please test them individually and report the results?

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)


View attachment "0001-ast-Use-VGACR17-sync-enable-and-VGACRB6-sync-off.patch" of type "text/x-patch" (2573 bytes)

View attachment "0001-ast-Use-VGACR17-sync-enable-and-VGASR01-screen-disab.patch" of type "text/x-patch" (2545 bytes)