linux-kernel - Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

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Message-ID: <adafy5k4pmx.fsf@cisco.com>
Date:	Fri, 25 May 2007 13:25:26 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Greg KH <gregkh@...e.de>, Jay Cliburn <jacliburn@...lsouth.net>,
	Grzegorz Krzystek <ninex@...eX.eu.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, ninex@...pl,
	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	Michael Ellerman <michael@...erman.id.au>,
	David Miller <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

 > > In addition to PCI INTx compatible interrupt emulation, PCI Express
 > > requires support of MSI or MSI-X or both. 
 > Which suggests that INTx support is required.
 > 
 > I do not find any wording that suggest the opposite.
 > I do see it stated that it is intended to EOL support for INTx at
 > some point.
 > 
 > Where did you see it mentioned that INTx was optional?

I don't see any requirement that a device that generates MSI
interrupts must also be able to signal the same interrupts via INTx.
The spec explicitly says:

    "All PCI Express device Functions that are capable of generating
    interrupts must support MSI or MSI-X or both."

but there is no corresponding explicit requirement that legacy INTx
mode be supported, so it certainly seems permitted for a device not to
generate INTx interrupts.  In fact as you alluded to, the spec says,

    "The legacy INTx emulation mechanism may be deprecated in a future
    version of this specification."

and I wouldn't think the intention would be for one version of the
spec to *require* something that is planned on being deprecated later.

And the Pathscale guys were pretty confident that their device was
compliant with the PCIe spec.

 - R.
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