Display black straight after KMS on Fedora 20 with gma500_gfx

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A friend has asked me to get Fedora 20 (3.14.2-200.fc20.x86_64) onto his Samsung nc110 netbook which has a GMA500 graphics chip. The problem is that as soon as Kernel Mode Setting begins, there's no video thereafter until reboot. Nothing, just a dim backlight behind a black LCD screen. Access via SSH always works.

 

I strongly suspect it's got something to do with KMS (though I might be wrong) because when booting from Arch 201405 install media (3.14.1-1-ARCH), display works fine every time, whereas the Fedora screen goes black at around the same point of kernel booting.

 

With Fedora (disabling the Plymouth splash), the kernel dmesg output disappears right after the point where KMS should change mode, never to be seen again. An external DVI monitor (from HDMI out) always works, but still nothing on the internal LCD. In this state, the cursor can move to the side and get lost, indicating that X knows there are two displays side-by-side, though nothing shows on the screen. (Moreover, to further confuse matters, once every 10 or 15 reboots, it actually all displays as if no problem, with exact same boot parameters).

 

Both Arch and Fedora load the same gma500_gfx and related modules (hope I haven't overlooked anything) as shown by lsmod. I've tried acpi=off (kernel panic). Tried xdriver=vesa (no difference). It doesn't matter whether it's x86 or x86_64 - same results.

 

This article describes what I believe to be the same issue with a different netbook, but appears he/she hasn't tried disabling the splash screen like I did (boot parameters 'rhgb' and 'splash').

ask.fedoraproject.org/en/question/44120/black-screen-on-fedora-20-right-after-grub/

 

It's just bizarre because the other two distros I have tried (Arch, BBQ) will work no problem. BBQ Linux even boots straight into X fine every time. It's JUST FEDORA. I have only tried Fedora 20 (no earlier).

 

I'm exhausted for ideas. Hope someone can advise me on setting Fedora 20 up to work right.

 

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