linux-kernel - Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

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Date:	Tue, 14 Nov 2006 20:30:36 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Linus Torvalds <torvalds@...l.org>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, tiwai@...e.de
Subject: Re: [PATCH] ALSA: hda-intel - Disable MSI support by default

 > That reminds me of a potential driver bug -- MSI-aware drivers need to
 > call pci_intx(pdev,0) to turn off the legacy PCI interrupt, before
 > enabling MSI interrupts.

Huh?  The device can't generate any legacy interrupts once MSI is
enabled.  As the PCI spec says:

    "While enabled for MSI or MSI-X operation, a function is prohibited
    from using its INTx# pin (if implemented) to request service (MSI,
    MSI-X, and INTx# are mutually exclusive)."

Although the MSI core does do pci_intx() for PCIe devices only, for
some reason I can't grok.

 > The only thing that has changed recently is that people are trying to
 > get it working on AMD/NV as well.  (Brice Goglin's stuff starting at
 > 6397c75cbc4d7dbc3d07278b57c82a47dafb21b5 in 'git log')

Actually NVidia/AMD was working on some systems long before that -- I
had it working at least 2 years ago.

 - R.
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