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Intel HD Graphics 3000 (Sandy Bridge) Maximum pclk 224MHz?

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Robert Schlabbach's picture
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Robert Schlabbach

Jun 29, 2014 - 03:54am

  • Hi,

    I'm trying to get the most out of my Core i5-2410M laptop connected to an UHD monitor via HDMI, on Ubuntu 14.04. Using try & error with the xrandr command, I was able to get 3840x2160 @25.2 Hz out of it using CVT with reduced blanking.

    The limit appears to be the "pclk" parameter, which will only go up to 224.xx MHz. Anything above that yields an error message that the CRTC could not be set.

    Q1: Is 224MHz pclk really the hard limit of the Intel HD Graphics 3000 hardware, or is it a limit of the Intel HD Graphics 3000 driver?

    Q2: If it's a limit of the driver, is it possible to circumvent / increase that limit somehow?

    Q3: Is it possible to _query_ the maximum pclk an X driver will accept? I tried all sorts of commands, yet found none which outputs this number...

     

    Jun 29, 2014 - 03:54am
  • Hi,

    I was wondering what Modeline you are using to get 3840x2160@25.2Hz?

    The highest rate I could get is 13.80Hz.

    Thanks,

    Jul 04, 2014 - 09:46pm
  • Use "cvt -r 3840 2160 60" to get a Modeline for 3840x2160 @60Hz with reduced blanking, then change the first number in the line (the pixel clock) from 533.00 to 224.99. If you manage to get higher pixel clock values working, please let me know...

    Jul 07, 2014 - 01:13pm
  • I think I found where this limit is coming from:
     
     
    Ironlake/Sandybridge definitions are found from line 256 on, and include:
     
            .p2 = { .dot_limit = 225000,
     
    There is a check for a value < dot_limit, so that would allow values up to 224.99, but not 225.00 - which is exactly what I observed.
     
    Now if one could figure out how to recompile this kernel module, it could be tried to increase the above value to e.g. 275000 and then try a Modeline with 266.00, which should yield 3840x2160 @30Hz...
    Jul 08, 2014 - 06:56am
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