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

From: Jocelyn Falempe <jfalempe@redhat.com>
To: Thomas Zimmermann <tzimmermann@suse.de>,
	Jani Nikula <jani.nikula@linux.intel.com>,
	airlied@redhat.com, kuohsiang_chou@aspeedtech.com,
	jammy_huang@aspeedtech.com
Cc: dri-devel@lists.freedesktop.org
Subject: Re: [PATCH] drm/ast: Fix default resolution when no monitor is connected on DP
Date: Thu, 6 Jul 2023 18:37:45 +0200	[thread overview]
Message-ID: <23d80964-d2d0-b688-e3cd-bf25a8135e5e@redhat.com> (raw)
In-Reply-To: <f4b4ab09-5f03-af3c-0e7f-44a248678be8@redhat.com>

On 06/07/2023 13:31, Jocelyn Falempe wrote:
> On 06/07/2023 12:26, Thomas Zimmermann wrote:
>> 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@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.
> 
> Oh, Thanks for the idea, I will try that.
> 

The result is that I get a black screen on the remote BMC. So maybe 
adding a remote/bmc connector will solve that.

-- 

Jocelyn