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[Bug 1428121] [NEW] Intel HDMI Audio not working with IOMMU enabled


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New ASRock Z97 Extreme 6 motherboard with an Intel i7 4790S and an
Nvidia GTX 650.

Host uses Intel IGD for video and HDMI audio out.

When I pass kernel flags 'intel_iommu=on' or 'intel_iommu=on,igfx_on'
HDMI audio no longer functions although the device and modules seem to
load and I cannot locate any error messages.  In this configuration
IOMMU functions as expected and I can successfully pass the Nvidia card
through to a KVM guest using VFIO.

As per this
(https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1223840) bug
report and the linked bugzilla thread I attempted to use kernel flag
'intel_iommu=on,igfx_off'.  This resolves the HDMI audio out but breaks
IOMMU as in VGA pass through generates DMA errors.

I'm running from a clean installation of 14.10 with no modifications to
the kernel or kvm, qemu, libvirt or virt-manager.

In either scenario above the analogue audio out continues to function, I
haven't tested the optical out as I have no hardware to do so.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: linux-image-3.16.0-31-generic 3.16.0-31.41
ProcVersionSignature: Ubuntu 3.16.0-31.41-generic 3.16.7-ckt5
Uname: Linux 3.16.0-31-generic x86_64
ApportVersion: 2.14.7-0ubuntu8.2
Architecture: amd64
 /dev/snd/controlC2:  kelvin     3468 F.... pulseaudio
 /dev/snd/controlC3:  kelvin     3468 F.... pulseaudio
 /dev/snd/controlC0:  kelvin     3468 F.... pulseaudio
 /dev/snd/controlC1:  kelvin     3468 F.... pulseaudio
CurrentDesktop: Unity
Date: Wed Mar  4 12:53:17 2015
HibernationDevice: RESUME=UUID=4d35060a-85c4-45fd-9f8e-530491588931
InstallationDate: Installed on 2015-02-26 (5 days ago)
InstallationMedia: Ubuntu-Server 14.10 "Utopic Unicorn" - Release amd64 (20141022.2)
MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M.
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.16.0-31-generic.efi.signed root=UUID=4914f227-6bb0-40bb-a781-9ad7111a996f ro intremap=no_x2apic_optout intel_iommu=on,forcedac pci-stub.ids=10de:11c8,10de:0e0b nomdmonddf nomdmonisw
 linux-restricted-modules-3.16.0-31-generic N/A
 linux-backports-modules-3.16.0-31-generic  N/A
 linux-firmware                             1.138.1
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/17/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: P1.70
dmi.board.name: Z97 Extreme6
dmi.board.vendor: ASRock
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP1.70:bd12/17/2014:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rnZ97Extreme6:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: To Be Filled By O.E.M.
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: To Be Filled By O.E.M.

** Affects: alsa-driver (Ubuntu)
     Importance: Medium
         Status: New

** Tags: amd64 apport-bug kernel-bug-exists-upstream latest-bios-1.70 utopic
Intel HDMI Audio not working with IOMMU enabled
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