HDMI audio stops working when X starts

[paul at intl.sbrk.co.uk]

Hi,

I've also sent this query to the alsa mailing list, but I think it's
more to do with the video driver than with alsa.

The problem is that HDMI audio works fine until I start X. The
driver for the Intel(R) Mobile Intel® GM45 Express Chipset
loads and I see a message in dmesg:
HDMI hot plug event: Presence_Detect=0 ELD_Valid=1
and sound output ceases. If I stop X, then I get
HDMI hot plug event: Presence_Detect=1 ELD_Valid=1
and sound output returns.

>From /var/log/Xorg.0.log I see:
Loading /usr/lib64/xorg/modules/drivers//intel_drv.so
..
(II) Primary Device is: PCI 00 at 00:02:0

Can someone tell me what this hot plug event signifies
and is there anything I can do to stop it disabling HDMI
audio?

I have the following devices:
# lspci|egrep -i 'audio|graphics'
00:02.0 VGA compatible controller: Intel Corporation Cantiga Integrated Graphics Controller (rev 07)
00:02.1 Display controller: Intel Corporation Cantiga Integrated Graphics Controller (rev 07)
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)
# lspci -n -s 2
00:02.0 0300: 8086:2a42 (rev 07)
00:02.1 0380: 8086:2a43 (rev 07)
# lspci -n -s 1b
00:1b.0 0403: 8086:293e (rev 03)
# lspci -vs 2
00:02.0 VGA compatible controller: Intel Corporation Cantiga Integrated Graphics Controller (rev 07) (prog-if 00 [VGA controller])
	Subsystem: Intel Corporation Cantiga Integrated Graphics Controller
	Flags: bus master, fast devsel, latency 0, IRQ 30
	Memory at fe400000 (64-bit, non-prefetchable) [size=4M]
	Memory at d0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 9080 [size=8]
	Capabilities: [90] Message Signalled Interrupts: Mask- 64bit- Count=1/1 Enable+
	Capabilities: [d0] Power Management version 3

00:02.1 Display controller: Intel Corporation Cantiga Integrated Graphics Controller (rev 07)
	Subsystem: Intel Corporation Device 2a42
	Flags: bus master, fast devsel, latency 0
	Memory at fe800000 (64-bit, non-prefetchable) [size=1M]
	Capabilities: [d0] Power Management version 3
# lspci -vs 1b
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)
	Subsystem: Micro-Star International Co., Ltd. Device 8180
	Flags: bus master, fast devsel, latency 0, IRQ 22
	Memory at fe9f8000 (64-bit, non-prefetchable) [size=16K]
	Capabilities: [50] Power Management version 2
	Capabilities: [60] Message Signalled Interrupts: Mask- 64bit+ Count=1/1 Enable-
	Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
	Capabilities: [100] Virtual Channel <?>
	Capabilities: [130] Root Complex Link <?>
	Kernel driver in use: HDA Intel
	Kernel modules: snd-hda-intel

Thanks,

Paul