24" Apple LED cinema, Z68 Pro3-M, iGPU, 11.04

**brandnamebob** · July 23rd, 2011

Originally Posted by asrock-z68

I'm assuming you are on a new snb 13" macbook pro that only supports the Intel HD 3000 graphics? Let me know how you make out. My solution was to run down to Best Buy and buy a cheap DVI monitor since I can't use my $1000 one.

Yes that is correct.

I was able to get it narrowed down to the kernel modesetting. It seems that the IOCTL is returning a Invalid Argument when the frequency is > 144.0 (154.0 would correspond to 60Hz)
I got it to work once at 77.0 (30Hz), but after restarting I can't get the monitor to recognize that it is on.

**asrock-z68** · July 23rd, 2011

Originally Posted by brandnamebob

Yes that is correct.

I was able to get it narrowed down to the kernel modesetting. It seems that the IOCTL is returning a Invalid Argument when the frequency is > 144.0 (154.0 would correspond to 60Hz) I got it to work once at 77.0 (30Hz), but after restarting I can't get the monitor to recognize that it is on.

My new DVI monitor is running at 148.5 MHz "1920x1080"x60.0. Wonder why it doesn't like the Apple DP?

Is this an intel-gfx issue or somewhere else?

**BicyclerBoy** · July 23rd, 2011

The OP could just buy a discrete video card with displayport..
A $50 nVidia card will out perform the intel GPU as well.

nVidia seems to be limiting displayport to the quadro cards & top end fermi but there were a few displayport versions of the older 9500 9600GT cards
AMD/ATI seem to have greater support for displayport.

**asrock-z68** · July 23rd, 2011

Originally Posted by BicyclerBoy

The OP could just buy a discrete video card with displayport..
A $50 nVidia card will out perform the intel GPU as well.

This is not going to work for brandnamebob. He has a brand spanking new sandy bridge Macbook Pro laptop (Intel HD 3000 iGPU only) with a killer external 27" LED Cinema Display.

I've asked for help over at intel-gfx@lists.freedesktop.org and have got no response so far.

**brandnamebob** · July 27th, 2011

OK, here is the problem: The EDID only lists one valid mode:
1920x1200 at 60Hz.
Which requires a clock rate of 154 at 24bit color.
The Apple LED Cinema Display also advertises only 2 available DisplayPort lanes at 2.7GHz.
But with 24bit color and only two lanes at 2.7GHz, 144 is the maximum clock rate.
Thus the mode is invalid as specified.

The reason the mode would be valid for Windows computers is that they degrade the display down to 18bit color (6bpc) automatically.

With Mac OSX the theory is that they utilize a proprietary DI-EXT extension to turn on the other two lanes for DisplayPort, thus giving Mac OSX a better experience using the display then other OSes.

To fix it in Linux, I hacked the intel-gfx kernel driver to automatically dither down to 6bpc and list the modes as valid. My fix is a pure hack and is not safe to redistribute, but if you want details I can post them. The reason it works on the other system with a nvidia card is I'm guessing that they automatically dither down to 6bpc.

I had a lot of help from the people in #intel-gfx on FreeNode. Without their help I could have never figured out the problem.

**asrock-z68** · July 27th, 2011

briandnamebob,

I'm glad the folks over at intel-gfx helped you with this. Not being a developer, I assumed I wasn't asking the right questions. Thanks for chasing this down. I'm assuming bpc = bits per channel. What's the relationship between channels and lanes? Do you think the folks over at intel-gfx will ultimately provide a fix? Or are snb Intel-igpu + Apple LED Cinema Display user's SOL?

I'd like to see the changes in the driver you made to make this work. Like I said I'm not a developer but I have made some changes to intel_display.c (gen6_enable_rps) and successfully recompiled the kernel to solve a gpu power issue. Maybe you could provide a diff or replacement driver for me to try.

I know the intel-gfx folks are working on some other DP issues and I'm happy to help in testing (with a little hand holding). I can also provide some information on how Windows 7 x64 handles this if someone can show me where to look. I'd like to contribute however I can.

**e8johan** · September 29th, 2011

I was just able to solve this in an easier manner. I simply add a new modeline, but with a lower refresh frequency.

Code:

xrandr --newmode "1920x1200_35.00" 107.02 1920 2008 2208 2496 1200 1201 1204 1225 -HSync +Vsync
xrandr --addmode DP1 "1920x1200_35.00"

Then I can pick it from the list of resolutions in the Display Settings dialog (in Kubuntu) and it works.

**altercation** · November 26th, 2011

Originally Posted by e8johan

I was just able to solve this in an easier manner. I simply add a new modeline, but with a lower refresh frequency.

Code:

xrandr --newmode "1920x1200_35.00" 107.02 1920 2008 2208 2496 1200 1201 1204 1225 -HSync +Vsync
xrandr --addmode DP1 "1920x1200_35.00"

Then I can pick it from the list of resolutions in the Display Settings dialog (in Kubuntu) and it works.

BRILLIANT. This solved it for me.

For what it's worth a refresh rate of 45 also works. Here's a simple script to generate the modelines for both 35 and 45 and add them for xrandr.

Code:

for _rate in 35 45
do
    _newmode="$(gtf 1920 1200 $_rate.00 | grep Modeline | sed "s/.*Modeline\s*\(.*\)/\1/")"
    _addmode="$(gtf 1920 1200 $_rate.00 | grep Modeline | sed "s/.*Modeline\s*\(\".*\"\).*/\1/")"
    eval xrandr --newmode $_newmode
    eval xrandr --addmode DP1 $_addmode
done

**kidneb** · May 14th, 2012

My 24" reports in fine on my nvidia MacBook(5,1) nvidia-stiettings reports 59,95 Hz. Runs fine, but some flickering in movies. (slightly off i assume).