Created attachment 115629 [details]
Panel datasheet

At this time I managed to get working video-stream to panel, but the timings is
obviously wrong. The main problem is Spread Spectrum somehow get disabled in
reinit cycle, and not enabled, so I just removed SS management and got blinking
noise on the screen.
Also I added some delays that necessary for this panel (maybe all another needs
it too). Due to attached datasheet on page 15 we got sequence of power-on and
power-off for this panel. Interesting this is Reset interval of 500ms which is
mandatory between power-off panel and powering it back on.

Now I'm trying to figure initial PLL setings that BIOS set before OS starts,
after that I'll try to fix this behaviour. I don't fully know vesa framebuffer
initialization, but as I understand, it get values from VBIOS/default BIOS
address space for VGA and trying to apply them. Moreover, when radeon KMS is
off I got fully different values of Modeline comparing to EDID.