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

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

What do you think?

Best regards,

-- 

Jocelyn