[Intel-gfx] DisplayPort testing for G45/GM45

Keith Packard keithp at keithp.com
Sat Mar 21 01:29:39 CET 2009

I finally managed to get my user-mode DisplayPort code working, and I'd
love to get some testing coverage as we move that code into the kernel.

It's on the 'display-port' branch and has only been tested on a Lenovo
X200s laptop (with DP in the dock) and a Dell 2408WFP monitor. Other
combinations would be very interesting to hear about.

There are a couple of known issues:

     1. You get bonus HDMI outputs. Because the driver isn't parsing the
        BIOS table data, it can't tell the difference between an HDMI
        output and a DP output; they both signal their presence using
        the same GPIO pin on the GMCH. In fact, on my X200s, I get three
        DP outputs and two HDMI outputs. It looks like the GPIO pins are
        completely unreliable here.
     2. Unplugging and re-plugging the monitor isn't 100%, you may have
        to try a couple of times. When DP is unplugged, some important
        state which is shared between the GMCH and the monitor gets lost
        (the "signal training settings"). The driver polls the monitor
        every 10 seconds to see if it's been disconnected and attempts
        to re-train the link, but that sometimes fails. Unplug the
        monitor, wait 10 seconds and plug it back in.

The kernel driver will be able to eliminate the 10 second polling
interval and use an interrupt to detect hot-plug. It will also need to
gain more BIOS table parsing code to correctly list the available

keith.packard at intel.com
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