linux-kernel - Re: Multiple MSI messages support

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Message-ID: <ada1wbbj215.fsf@cisco.com>
Date:	Tue, 30 Oct 2007 22:17:42 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	"Shawn Jin" <shawnxjin@...il.com>
Cc:	"Jeff Garzik" <jeff@...zik.org>, linux-kernel@...r.kernel.org
Subject: Re: Multiple MSI messages support

 > My interpretation of this statement is that you have to use MSIX if
 > multiple MSI messages are required on Linux.

Yes, Linux only supports multiple messages with MSI-X, not MSI.  This
is an architectural limitation of "Intel-style" interrupt controllers
(x86 and ia64).  It is also a limitation of the Linux's MSI API, since
there are platforms and devices for which an OS could allocate
multiple MSI messages, but Linux has no interface that allows that.

The historical reason for the Linux interface is simply that Intel
platforms were the first place that MSI/MSI-X was supported.

 - R.
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