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

[Jocelyn Falempe]

On 13/02/2025 15:01, Thomas Zimmermann wrote:
> 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.

Ok, I will try to make something. DMI quirk is less flexible, but the 
regression is a bit old, so I hope there won't be much other hardware 
affected.

Best regards,

-- 

Jocelyn

> 
> Best regards
> Thomas
> 
>>
>> Best regards,
>>
>