[Dri-users] gma500: wrong pixel clock on LVDS (half the correct frequency)

[Paulo Marques]

Hi all,

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 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 32MHz. This probably 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 
nonsensical questions...

Thanks in advance for any help,

Paulo Marques