linux-kernel - Re: Kernel Options: To use MSI-X or not?

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Date:	Wed, 04 Nov 2009 12:36:51 -0500
From:	Valdis.Kletnieks@...edu
To:	Justin Piszcz <jpiszcz@...idpixels.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Kernel Options: To use MSI-X or not?

On Wed, 04 Nov 2009 11:53:18 EST, Justin Piszcz said:

> Example, 3ware cards/Intel Audio Drivers you can use MSI-X instead of 
> having several devices use/share an interrupt.
> 
> What are the pros/cons to using MSI-X vs. having devices share an IRQ?

Cons: Sometimes, you'll find a device that claims to support MSI but in fact is
to some extent borked...

I'm the proud owner of a Dell Latitude D820, which includes this PCI:

00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)
        Subsystem: Dell Device 01cc
        Flags: bus master, fast devsel, latency 0, IRQ 30
        Memory at efffc000 (64-bit, non-prefetchable) [size=16K]
        Capabilities: [50] Power Management version 2
        Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [130] Root Complex Link <?>
        Kernel driver in use: HDA Intel

However, actually trying to enable MSI gets me this at some pseudo-random
time after booting (one for each of 7 boots):

[    4.519264] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[   22.788015] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x008f0c00
[    4.719263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[   12.497263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[  815.350265] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[  595.171267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
[    4.968263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900

(Am slightly mystified about the resets at 4 and 12 seconds - at that point,
we're not up far enough to actually try to use the audio. I suspect udev trying
to initialize the card - except sometimes it works and runs just fine with
MSI for quite some time:

[14267.701267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[12841.892050] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[10647.783274] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x001f1500
[15091.102034] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
[20085.955293] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0700



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