radeon: Regression between v3.6-rc4 and v3.6-rc6: unable to allocate a PPLL

[Andres Freund <andres@anarazel.de>]

Hi,

While debugging another issue I upgraded from v3.6-rc4 to latest git (which 
exactly is v3.6-rc6). After X started up one of my three monitors blacked out. 
A look into the kernel log revealed:
[drm:radeon_atom_pick_pll] *ERROR* unable to allocate a PPLL

During that first start I tried to correct that using xrand, which failed. 
After restarting X (gdm) once more the monitor was still blank, the error was 
still logged, but could be enabled by using xrandr. A bit strange.

A quick look into git revealed:

$ git log --pretty=short v3.6-rc4.. drivers/gpu/drm/radeon/
commit f492c171a38d77fc13a8998a0721f2da50835224
Author: Christian König <deathsimple@vodafone.de>

    drm/radeon: make 64bit fences more robust v3

commit 985f61f7ee647ad570c05eab0b74915da2ac8e19
Author: Alex Deucher <alexander.deucher@amd.com>

    drm/radeon: rework pll selection (v3)

The latter seems to be a probably cause. Anything I can do to diagnose the 
issue?

$ xrandr|grep -E 'connected|Screen'
Screen 0: minimum 320 x 200, current 4960 x 1920, maximum 16384 x 16384
DVI-1 connected 2560x1600+1200+0 (normal left inverted right x axis y axis) 
641mm x 401mm
DisplayPort-0 connected 1200x1920+0+0 left (normal left inverted right x axis y 
axis) 518mm x 324mm
HDMI-0 disconnected (normal left inverted right x axis y axis)
DVI-0 connected 1200x1920+3760+0 left (normal left inverted right x axis y 
axis) 518mm x 324mm

# lspci -v -s 08:00.0
08:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Barts 
XT [Radeon HD 6800 Series] (prog-if 00 [VGA controller])
	Subsystem: PC Partner Limited Device 174b
	Flags: bus master, fast devsel, latency 0, IRQ 76
	Memory at d0000000 (64-bit, prefetchable) [size=256M]
	Memory at fbec0000 (64-bit, non-prefetchable) [size=128K]
	I/O ports at e000 [size=256]
	Expansion ROM at fbea0000 [disabled] [size=128K]
	Capabilities: [50] Power Management version 3
	Capabilities: [58] Express Legacy Endpoint, MSI 00
	Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
	Capabilities: [150] Advanced Error Reporting
	Kernel driver in use: radeon

Greetings,

Andres