On Mon, Sep 17, 2012 at 6:28 PM, Takashi Iwai <tiwai at suse.de> wrote: > At Mon, 17 Sep 2012 18:21:47 +1000, > Dave Airlie wrote: >> >> On Mon, Sep 17, 2012 at 6:16 PM, Takashi Iwai <tiwai at suse.de> wrote: >> > Hi Adam, >> > >> > At Fri, 14 Sep 2012 11:25:03 -0400, >> > Adam Jackson wrote: >> >> >> >> On 9/14/12 10:19 AM, Takashi Iwai wrote: >> >> > Hi, >> >> > >> >> > we've got a machine showing a ghost DP2 output on a docking station. >> >> > The docking station has only one DP port and it's connected to DP1. >> >> > As a result, we get an DP2 active output containing the bogus VESA >> >> > standard modes 1024x768, 800x600, 640x480 although it's not connected >> >> > at all. >> >> > >> >> > Looking a bit deeply on it, it seems that the connector gives actually >> >> > the valid DPCD. So intel_dp_detect() returns >> >> > connector_status_connected. But since there is no real connection, >> >> > EDID isn't obtained. Thus of course no valid modes set. >> >> >> >> Can you be more specific here? What DPCD does it return? >> > >> > It shows "DPCD: 110a820100030181" >> >> I don't see how it can be a floating port if something is answering >> DPCD, or how it could be a hardware problem. Like it doesn't seem >> likely they terminated the port with a special DP chip. > > The problem is that you have no DP output there in reality. So, when > you plug the docking station, GNOME sets up the screen with a bogus DP > output, either in an extended mode with a non-existing screen or a > clone mode with a wrong low resolution. Yes I understand the problem, I'm disagreeing with your diagnosis of what the problem is, since DPCD response means something is there. DPCD comes from the other end of the cable. > >> Though you'd have to decode the DPCD to see what it is. > > Hmm, but isn't it the check of EDID existence enough? No thats a hack, that we might use, but I can't imagine a DP->VGA with a EDID-less VGA device producing an EDID, whereas it will produce a DPCD. > Checking DPCD bits might work, but I have no exact spec of DPCD, so no > idea whether the above is really wrong or not. Is there a VGA port on the docking station, it might have a DP->VGA in it, or dual-link DVI port. Dave.
