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

From: Jani Nikula <jani.nikula@linux.intel.com>
To: Jocelyn Falempe <jfalempe@redhat.com>,
	tzimmermann@suse.de, 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, 06 Jul 2023 12:32:46 +0300	[thread overview]
Message-ID: <87h6qhxu4h.fsf@intel.com> (raw)
In-Reply-To: <ed075f2f-861d-74d1-efc0-5baa2cd601fd@redhat.com>

On Thu, 06 Jul 2023, Jocelyn Falempe <jfalempe@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@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.

> 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,

-- 
Jani Nikula, Intel Open Source Graphics Center