drm/ast regression, when upgrading from v6.3 to v6.6

[Thomas Zimmermann]

Hi

Am 13.02.25 um 14:33 schrieb Jocelyn Falempe:
> Hi Thomas and Jammy,
>
> I've got a regression report, and it's caused by 
> https://patchwork.freedesktop.org/patch/540015/
> On this ast2600 server, the firmware says it has a DP output, but 
> physically, there is only one VGA output.
> Before this commit, "ast->tx_chip_types |= BIT(AST_TX_ASTDP)" means it 
> will have both VGA and DP configured, but after this changed to 
> "ast->tx_chip_types = AST_TX_ASTDP_BIT" and the VGA connector disappear.

Having multiple outputs (besides the virtual BMC) was never really 
supported. DRM userspace also doesn't really support it. You likely 
remember that we had problems when the BMC was a separate output.

> The EDID of the VGA monitor is not read anymore, and a wrong 
> resolution is setup causing a blank screen.
>
> Of course fixing the firmware would be the best solution, it's not 
> always possible.
>
> I'm considering different options:
> - Add a kernel module parameter to override the tx_chip_types, 
> something like "ast.output=vga"

No parameters please. If we give people parameters, they will configure 
the hell out of them and then complain if it doesn't work. And we never 
get rid of parameters, because "there's users".

> - Add a DMI quirk, to force vga on this particular motherboard.

That could work.

>
> What do you think?

I think I saw another bit in the HW docs that hints towards a VGA 
output, but I cannot find it anymore. Still, I have VGA and DP on my 
test board. There's gotta be a way of switching between them.

Unless something else shows up, let's to the DMI quirk. It should also 
be easy to  backport.

Best regards
Thomas

>
> Best regards,
>

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