From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932298Ab0JZRJ2 (ORCPT <rfc822;w@1wt.eu>);
	Tue, 26 Oct 2010 13:09:28 -0400
Received: from rcsinet10.oracle.com ([148.87.113.121]:36956 "EHLO
	rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1753379Ab0JZRJ0 (ORCPT
	<rfc822;<linux-kernel@vger.kernel.org>>);
	Tue, 26 Oct 2010 13:09:26 -0400
Date: Tue, 26 Oct 2010 13:08:41 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: xen-devel@lists.xensource.com, Ian Campbell <ian.campbell@citrix.com>,
        Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>,
        linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        mingo@elte.hu, tglx@linutronix.de
Subject: Re: [Xen-devel] Re: [PATCH 1/5] xen: events: use
 irq_alloc_desc(_at) instead of open-coding an IRQ allocator.
Message-ID: <20101026170841.GA10708@dumpdata.com>
References: <1288023736.11153.40.camel@zakaz.uk.xensource.com>
 <1288023813-31989-1-git-send-email-ian.campbell@citrix.com>
 <20101025173522.GA5590@dumpdata.com>
 <4CC60CB7.3070005@goop.org>
 <20101026141739.GA9557@dumpdata.com>
 <4CC70583.2050503@goop.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4CC70583.2050503@goop.org>
User-Agent: Mutt/1.5.20 (2009-06-14)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> In that case we should use dynamic allocation for everything.  Or try to
> work out distinct irq ranges for different interrupts if you really want
> to keep irq==gsi.

Some little alarm bells are ringing in the back of my head about irq != gsi.

I think the issue was the permission. When a PCI device is allocated to the
PV guest, we do a bunch of xc_* calls to allow the domain to use the BARs
and the IRQ. I believe when the guest boots and tries to map the
event channel with the physical IRQ, one of the arguments is that GSI. And
if we provide a bogus GSI, well, we won't get the INTx to the guest.

As you mentioned, Stefano's patch add a new element to the tuple that can
contain the GSI value. At which point we can make the guest IRQ != GSI,
as long as we can contain the <gsi, event channel> mapping present so
that for the hypercalls we can give it the right GSI.

The MSI/MSI-X use a completly different mechanism that does not all
of this complication, so we are OK with that.

.. snip ..

> d) dynamically allocate all irqs for all event channel types.

<nods> Ok, you sold me on this idea.