radeon DRM module, AMD A-6 APU, no signal recovery after DPMS Off (can be worked around)

[wdraxinger.maillist at draxit.de (Wolfgang Draxinger)]

Hi,

I observe the following annoyance in my newly built HTPC (specs, lspci
etc. at the end of the mail) when using the radeon kernel module with
KMS enabled: After the display goes into DPMS Off, returning to DPMS On
mode will not return a signal to the display (without further
action). /sys/class/drm/card0-VGA-1/dmps reports the status as it
should be and the system stays stable and usable. The monitor is
connected via analogue signal on the VGA port (digital transmission is
not an option for this system).

The display signal can be brought back by performing a modeswitch (ATM
I'm working around this problem with a small helper that
polls /sys/class/drm/card0-VGA-1/dpms for a Off->On transition and
quickly changes the vertical clock to a helper frequency and back).
Hence I suspect that the CRTC is not properly brought back into
operation; I assume the modeswitch does bring it back into a sane
state.

I suggest a workaround/fix in which the CRTC is fully reinitialized
when doing a DPMS transition to On state.

Summary problem description:
AMD A-6 APU, with integrated Radeon core, Linux 3.5 radeon DRM/DRI2
kernel module ? Video signal does not come back after DPMS state
transistion into On state. Happens with X11 and the framebuffer console
alike. Switching the video mode brings back the signal.

System information:
GPU: AMD A-6 3500 APU integrated Radeon HD 6530D

Arch Linux
# uname -a
Linux beyla 3.5.3-1-ARCH #1 SMP PREEMPT Sun Aug 26 09:14:51 CEST 2012 x86_64 GNU/Linux

# pacman -Q | grep ati
ati-dri 8.0.4-3
xf86-video-ati 1:6.14.6-1

# lspci
00:00.0 Host bridge: Advanced Micro Devices [AMD] Family 12h Processor Root Complex
00:01.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI BeaverCreek [Radeon HD 6530D]
00:02.0 PCI bridge: Advanced Micro Devices [AMD] Family 12h Processor Root Port
00:10.0 USB controller: Advanced Micro Devices [AMD] Hudson USB XHCI Controller (rev 03)
00:10.1 USB controller: Advanced Micro Devices [AMD] Hudson USB XHCI Controller (rev 03)
00:11.0 SATA controller: Advanced Micro Devices [AMD] Hudson SATA Controller [AHCI mode] (rev 40)
00:12.0 USB controller: Advanced Micro Devices [AMD] Hudson USB OHCI Controller (rev 11)
00:12.2 USB controller: Advanced Micro Devices [AMD] Hudson USB EHCI Controller (rev 11)
00:13.0 USB controller: Advanced Micro Devices [AMD] Hudson USB OHCI Controller (rev 11)
00:13.2 USB controller: Advanced Micro Devices [AMD] Hudson USB EHCI Controller (rev 11)
00:14.0 SMBus: Advanced Micro Devices [AMD] Hudson SMBus Controller (rev 13)
00:14.1 IDE interface: Advanced Micro Devices [AMD] Hudson IDE Controller
00:14.2 Audio device: Advanced Micro Devices [AMD] Hudson Azalia Controller (rev 01)
00:14.3 ISA bridge: Advanced Micro Devices [AMD] Hudson LPC Bridge (rev 11)
00:14.4 PCI bridge: Advanced Micro Devices [AMD] Hudson PCI Bridge (rev 40)
00:14.5 USB controller: Advanced Micro Devices [AMD] Hudson USB OHCI Controller (rev 11)
00:15.0 PCI bridge: Advanced Micro Devices [AMD] Device 43a0
00:18.0 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 0 (rev 43)
00:18.1 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 1
00:18.2 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 2
00:18.3 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 3
00:18.4 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 4
00:18.5 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 6
00:18.6 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 5
00:18.7 Host bridge: Advanced Micro Devices [AMD] Family 12h/14h Processor Function 7
01:00.0 Multimedia video controller: Conexant Systems, Inc. CX23887/8 PCIe Broadcast Audio and Video Decoder with 3D Comb (rev 04)
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 06)


Regards,

Wolfgang