[Bug 78562] New: [gma500] wrong pixel clock on LVDS (half the correct frequency)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78562

          Priority: medium
            Bug ID: 78562
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [gma500] wrong pixel clock on LVDS (half the correct
                    frequency)
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: pmarques at masterguardian.com
          Hardware: x86 (IA32)
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

I have a embedded PC system here that has an Atom Z510. The system includes a
GMA500 graphics chip.

The display is connected through the LVDS port and has a resolution of
1024x768.

The system works ok in Windows and painfully slowly in Linux with the vesa
driver, but without any flicker.

Using the gma500 driver, the pixel clock seems to be half of what it should be
(measured with an oscilloscope). When the image is good the pixel clock is
around 65MHz. When the gma500 driver sets the resolution the pixel clock goes
to around 32MHz. This gives a frame rate of around 30Hz which explains the
horrible screen flicker. The performance is quite good, though.

I tried running xrandr to create new modes, but the pixel clock is always
wrong, no matter what I tried.

The kernel version is 3.12.1. I looked at the git repository log to see if
anything changed in the meanwhile that could affect this, but nothing popped
up.

Can you give me some pointers to what I should try next? Some obscure kernel
parameter? Do you need more information?

The linux graphics system changed a bit over the last few years (KMS, etc.) and
I missed some of the changes, so please bare with me if I ask silly
questions...

Thanks in advance for any help.

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