From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964930AbXC2FDc (ORCPT ); Thu, 29 Mar 2007 01:03:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965951AbXC2FDc (ORCPT ); Thu, 29 Mar 2007 01:03:32 -0400 Received: from ozlabs.org ([203.10.76.45]:54843 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964930AbXC2FDb (ORCPT ); Thu, 29 Mar 2007 01:03:31 -0400 Subject: Re: [PATCH 14/21] MSI: Use a list instead of the custom link structure From: Michael Ellerman Reply-To: michael@ellerman.id.au To: "Eric W. Biederman" Cc: linux-pci@atrey.karlin.mff.cuni.cz, Greg Kroah-Hartman , "David S. Miller" , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org, Andrew Morton , daniel.e.wolstenholme@intel.com In-Reply-To: References: <20070322105343.3B358DDF6D@ozlabs.org> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-YUAR3J540GEZy43s4XX7" Date: Thu, 29 Mar 2007 15:03:29 +1000 Message-Id: <1175144609.16660.33.camel@concordia.ozlabs.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --=-YUAR3J540GEZy43s4XX7 Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Wed, 2007-03-28 at 00:29 -0600, Eric W. Biederman wrote: > Michael Ellerman writes: >=20 > > The msi descriptors are linked together with what looks a lot like > > a linked list, but isn't a struct list_head list. Make it one. > > > > The only complication is that previously we walked a list of irqs, and > > got the descriptor for each with get_irq_msi(). Now we have a list of > > descriptors and need to get the irq out of it, so it needs to be in the > > actual struct msi_desc. We use 0 to indicate no irq is setup. > > > > At some point after a pci_dev is created we need to initialise its > > msi_list. pci_device_add() looks like the right place to do that, altho= ugh > > I'm not convinced it's 100% safe. In drivers/char/agp/alpha-agp.c we cr= eate > > a pci_dev and I don't see that it ever gets passed to pci_device_add(),= but > > we probably don't care. >=20 > Well that one appears to be a dummy place holder and probably should at > least have a kzalloc to initialize all of the fields to know values. >=20 > Regardless the normal pci device allocation does use kzalloc so we will > have well defined if not beautiful behavior if we try and use it. >=20 > Until we have a case where we need to use the msi_list outside of=20 > where we enable and disable msi we should be perfectly fine initializing > the list somewhere inside of pci_enable_msi, and pci_enable_msix. > With dev->msi_enabled and dev->msix_enabled serving as flags to the > rest of the world that it is safe to look at the list. >=20 > It certainly sounds safer to me then becoming to closely coupled with > code that doesn't really care about how msi works. Heck even though > we repeat the call twice I bet it will even be less code. I thought about doing it in the MSI enable methods, but I think it really belongs in the (nonexistant) routine that allocs and sets up a pci_dev. I think it's pretty dicy to be passing around a pci_dev with an uninitialised msi_list. Even if currently no code outside the MSI enable methods looks at it, I think we're asking for bugs in the future. So I'll do a patch which adds alloc_pci_dev(), update the callers, and then put the msi_list initialisation in there. > > --- msi-new.orig/include/linux/msi.h > > +++ msi-new/include/linux/msi.h > > @@ -1,6 +1,8 @@ > > #ifndef LINUX_MSI_H > > #define LINUX_MSI_H > > =20 > > +#include > > + > > struct msi_msg { > > u32 address_lo; /* low 32 bits of msi message address */ > > u32 address_hi; /* high 32 bits of msi message address */ > > @@ -24,10 +26,8 @@ struct msi_desc { > > unsigned default_irq; /* default pre-assigned irq */ > > }msi_attrib; > > =20 > > - struct { > > - __u16 head; > > - __u16 tail; > > - }link; > > + int irq; > This should be "unsigned int irq" Oops, I'll fix that. cheers --=20 Michael Ellerman OzLabs, IBM Australia Development Lab wwweb: http://michael.ellerman.id.au phone: +61 2 6212 1183 (tie line 70 21183) We do not inherit the earth from our ancestors, we borrow it from our children. - S.M.A.R.T Person --=-YUAR3J540GEZy43s4XX7 Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) iD8DBQBGC0ihdSjSd0sB4dIRAkkCAJ41/b8NnckoqwWF6Zhj1LkVA1OREwCfVNp3 zwLFAwP+npb6hg735Yr3qZM= =eEDC -----END PGP SIGNATURE----- --=-YUAR3J540GEZy43s4XX7--