[coreboot] question on libgfxinit DP port number

[Nico Huber]

On 18.07.2017 11:05, Iru Cai wrote:
> Thanks, Nico
> 
> 
> On 2017年07月18日 16:20, Nico Huber wrote:
>> Hi Iru,
>>
>> On 18.07.2017 09:28, Iru Cai wrote:
>>> Hi,
>>>
>>> I found the mainboard DP port doesn't have output before kernel starts in
>>> hp/2570p (https://review.coreboot.org/c/20489/). After I added DP3 and
>>> HDMI3 in port list, the DP port had output, and cbmem log said it's DP3.
>>> However, xrandr says this port is DP2. What is the problem?
>> libgfxinit only knows about physical ports (i.e. how they are ordered*
>> in the datasheet). Linux ignores ports that aren't strapped to be active
>> (or are disabled by VBT) and renumbers the ports to fill the holes.
>>
>> Nico
>>
>> * The numbering is not perfect. As historically VGA was the first port
>>   (port A in datasheets), digital ports are counted from B, so DP1 is
>>   port B, DP2 is port C, etc.
> 
> Now I found /sys/class/drm_dp_aux_dev/drm_dp_aux{0,1} (Linux 4.4) and
> `cat /sys/class/drm_dp_aux_dev/*/name` gives me:
>   DPDDC-B
>   DPDDC-D
> 
> So should the ports be DP1 and DP3?

Yes, likely (if mainboard and/or Linux aren't super weird and twist this
too).

Nico