From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750704AbWGKHtX (ORCPT ); Tue, 11 Jul 2006 03:49:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750703AbWGKHtX (ORCPT ); Tue, 11 Jul 2006 03:49:23 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:23190 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S1750704AbWGKHtX (ORCPT ); Tue, 11 Jul 2006 03:49:23 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Segher Boessenkool Cc: Benjamin Herrenschmidt , Andrew Morton , Dave Olson , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] Initial generic hypertransport interrupt support. References: <1152571162.1576.122.camel@localhost.localdomain> <1152595205.6346.26.camel@localhost.localdomain> <9ABD3384-5829-4365-988C-43310D374CE5@kernel.crashing.org> Date: Tue, 11 Jul 2006 01:48:33 -0600 In-Reply-To: <9ABD3384-5829-4365-988C-43310D374CE5@kernel.crashing.org> (Segher Boessenkool's message of "Tue, 11 Jul 2006 09:29:29 +0200") Message-ID: User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Segher Boessenkool writes: >> As for supporting multiple irqs in plain MSI mode, I don't think >> we want to do that. The problem is that multiple interrupts >> in msi mode cannot be individually routed. > > On some(/many/most) platforms that isn't a problem. Platforms > for which it is can just refuse to allocate more than one MSI > at once. It is a problem on all platforms that currently implement MSI. >> I think we really want >> to encourage vendors who are building cards with multiple MSI irqs >> to use MSI-X. MSI-X has a lot fewer ugly special cases and all >> architectures can individually route the irqs. > > We still should support whatever hardware already exists, if > possible. Which hardware is this a problem for? MSI and MSI-X only guarantee the availability of 1 irq if I recall correctly. More are a bonus so cards should be able to fall back to a single irq mode. >> If there are interesting cards that support just MSI mode and really >> need more than one irq I would be happy to reconsider that decision >> but my impression was that plain MSI was basically not quite flexible >> enough to really be interesting, and supporting just one MSI irq was >> ok but any more would lead to all kinds of strange special cases. > > Individual drivers can deal with those special cases if they are device- > specific; and the platform can just refuse to do more than one MSI if > something platform-specific would prevent correct operation. > > It would be nice to have the MSI and MSI-X interfaces have the same > calling convention; in fact, they can probably be folded into one. Examples? details? patches? Part of the problem with plain MSI is that you can't mask irqs at the source, in a generic way. How do your ideas compare with my hypertransport irq implementation? Eric