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

[Jocelyn Falempe]

On 06/07/2023 11:32, Jani Nikula wrote:
> On Thu, 06 Jul 2023, Jocelyn Falempe <jfalempe at redhat.com> wrote:
>> 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.
> 
> \o/
> 
>> 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 ?
> 
> I couldn't say, but having the driver lie about the connected status to
> make it work feels wrong.

Yes, so maybe a better way would be to add a remote/bmc connector, with 
proper default resolution ?
That will better reflect what the hardware does.

-- 

Jocelyn

> 
>> 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.
> 
> Thanks,
> Jani.
> 
> 
>>
>> Best regards,
>