Issue with DRM and "reimplement IDR and IDA using the radix tree"

[Alexandre Courbot]

Hi Matthew,

Trying the latest -next on the Jetson TK1 board (with two different DRM
devices and display and render), I noticed that the GPU device probe
always failed with error -ENOSPC. After investigating I figured out that
this was due to the minor device allocation failing when a second DRM
device is added.

More precisely, when drm_minor_alloc() is called with DRM_MINOR_PRIMARY
(0) as argument for a second time, the call to idr_alloc() (which has a
requested range of 0..64) fails instead of returning 1 as expected. Note
that the first call is successful.

Reverting "reimplement IDR and IDA using the radix tree" on 20161213's
next fixes the issue for me, suggesting a bug may have slipped in there.

Not sure how this could be fixed, so reporting the issue for now in case
it is not known yet.

Cheers,
Alex.