No screens after (WW) Falling back to old probe method for modesetting

Rafał Miłecki zajec5 at
Tue Jun 12 08:01:19 PDT 2012

2012/6/11 Rafał Miłecki <zajec5 at>:
> I'm trying to switch from fbdev to modesetting for my AMD Southern
> Islands VERDE card. Of course I've KMS running just fine, radeon
> module loads and sets correct resolution, dmesg looks alright
> Unfortunately Xorg doesn't start after forcing "modesetting", AFAIU
> the driver doesn't provide any screens/modes. It looks like this:
> (II) Loading /usr/lib/xorg/modules/drivers/
> (WW) Falling back to old probe method for modesetting
> (II) UnloadModule: "modesetting"
> (II) Unloading modesetting
> (EE) Screen(s) found, but none have a usable configuration.
> Can you give me any tip on this? My X.Org X Server is 1.10.4, I'm
> using xf86-video-modesetting from today's git. Any patch/trick to
> debug this issue?

I don't think old X server is an issue here. The function to focus on
is probe_hw_pci.

This function calls "open_hw" which opens /dev/dri/card0 and return fd
(9 in my case, irrelevant). Then comes the moment when probe_hw_pci
id = drmGetBusid(fd);
devid = ms_DRICreatePCIBusID(pdev);

The first one returns NULL, the second one returns "pci:0000:03:00.0".
As the "id" is NULL (empty string) probe_hw_pci returns false and the
rest fails.

I can't say why drmGetBusid returns NULL. My drm is from yesterday's
git and DRM_IOCTL_GET_UNIQUE isn't something bleeding edge AFAIK.
Hacking probe_hw_pci to return TRUE allows me start X with


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