[PATCH] drm/ast: Fix default resolution when no monitor is connected on DP

[Thomas Zimmermann]

Hi

Am 06.07.23 um 11:16 schrieb Jocelyn Falempe:
> On 04/07/2023 18:45, Jocelyn Falempe wrote:
>> On 04/07/2023 16:54, Jani Nikula wrote:
>>> On Fri, 23 Jun 2023, Jocelyn Falempe <jfalempe at redhat.com> wrote:
>>>> Since commit fae7d186403e ("drm/probe-helper: Default to 640x480 if no
>>>>   EDID on DP")
>>>> The default resolution is now 640x480 when no monitor is connected.
>>>> But Aspeed graphics is mostly used in servers, where no monitor
>>>> is attached. This also affects the "remote" resolution to 640x480, 
>>>> which is
>>>> inconvenient, and breaks the anaconda installer.
>>>> So when no EDID is present, set 1024x768 as preferred resolution.
>>>
>>> This conflates "monitor connected" and "EDID present", which are not
>>> necessarily the same thing.
>>>
>>> The fallback in drm_helper_probe_single_connector_modes() is for no
>>> modes, but connector status is connected or unknown.
>>
>> When debugging the issue, I found it surprising that the status is 
>> "connected" when nothing is plugged in the DP port.
>>>
>>> You could add a connector ->detect callback that returns disconnected
>>> when there's no display, and the problem should go away. If there's no
>>> ->detect callback, it'll default to connected.
>>
>> ok, I'll try that. I don't know how the hardware detect something is 
>> connected, but looking at the dp code, maybe checking 
>> "AST_IO_CRTC_PORT,0xDC, ASTDP_LINK_SUCCESS" would be good enough.
> 
> I've tested this approach, and it works. But on the server I'm testing, 
> there are VGA and DP output. I think on a server that has only one DP 
> output, if no monitor is connected, then no modes will be reported to 
> userspace, and the remote BMC may not work ?

You could out-comment the VGA code in the ast driver for testing.

Best regards
Thomas

> 
> Also I don't have physical access to the server, so I only tested when 
> no monitor is plugged.
> 
> I will send shortly a v2 with this change, so others can help me test 
> this case.
> 
> 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
HRB 36809 (AG Nuernberg)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20230706/9b87bec6/attachment-0001.sig>