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

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Date:	Fri, 25 May 2007 10:10:13 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Roland Dreier <rdreier@...co.com>
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.

Roland Dreier <rdreier@...co.com> writes:

>  >  > - In spec hardware does not require MSI to generate interrupts
>  >  >   Which leaves enabling MSI optional.
>  > 
>  > Actually at least the Qlogic/Pathscale PCI Express ipath adapters
>  > cannot generate INTx interrupts -- they definitely do require MSI to
>  > operate.
>
> Oh yeah... when I first found out about this, I rechecked the PCI
> Express spec and found that in fact legacy INTx interrupts are
> optional.  So the ipath adapters that require MSI do conform to the
> spec.

Hmm...

I find in section 6.1:
> 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 do see it clearly stating that MSI is the preferred mechanism from
pci express.

Eric
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