From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753385AbaFDNm0 (ORCPT ); Wed, 4 Jun 2014 09:42:26 -0400 Received: from mail-wg0-f50.google.com ([74.125.82.50]:56689 "EHLO mail-wg0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753249AbaFDNmW (ORCPT ); Wed, 4 Jun 2014 09:42:22 -0400 Date: Wed, 4 Jun 2014 15:39:36 +0200 From: Thierry Reding To: Will Deacon Cc: Arnd Bergmann , Hiroshi Doyu , Rob Herring , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Cho KyongHo , Grant Grundler , Dave P Martin , Marc Zyngier , Joerg Roedel , Stephen Warren , "devicetree@vger.kernel.org" , Linux IOMMU , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-samsung-soc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings Message-ID: <20140604133934.GD28484@ulmo> References: <1400877218-4113-1-git-send-email-thierry.reding@gmail.com> <4545972.cM7IP1qTXQ@wuerfel> <87tx87rrp2.fsf@nvidia.com> <4462924.8iRbdkOPp7@wuerfel> <20140601095546.GA8625@arm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="T7mxYSe680VjQnyC" Content-Disposition: inline In-Reply-To: <20140601095546.GA8625@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --T7mxYSe680VjQnyC Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Jun 01, 2014 at 10:55:46AM +0100, Will Deacon wrote: > On Fri, May 30, 2014 at 08:54:37PM +0100, Arnd Bergmann wrote: > > On Friday 30 May 2014 22:29:13 Hiroshi Doyu wrote: > > > Tegra,SMMU has a similar problem and we have used a fixed size bitmap= (64 > > > bit) to afford 64 stream IDs so that a single device can hold multiple > > > IDs. If we apply the same bitmap to the above exmaple: > > >=20 > > > iommu { > > > /* the specifier represents the ID of the master */ > > > #address-cells =3D <1>; > > > #size-cells =3D <0>; > > > }; > > >=20 > > > master@a { > > > ... > > > iommus =3D <&smmu (BIT(1) | BIT(2) | BIT(3))>; # IDs = 1 2 3 > > > }; > > >=20 > > > master@b { > > > ... > > > iommus =3D <&smmu BIT(4)>; # ID 4 > > > }; > > >=20 > > > The disadvantage of this is that this limits the max number of stream= IDs > > > to support. If # of streamID is increased later more than 64, this > > > format cannot cover any more. You have to predict the max # of stream= IDs > > > in advance if steamID is statically assigned. > > >=20 > >=20 > > Well, the iommu specific binding could allow a variable #address-cells. > > That way, you just need to know the number of stream IDs for that insta= nce > > of the iommu. >=20 > In general, though, the SMMU will be able to support a large number of > stream IDs (say a 16-bit space). The restriction we're interested in here= is > how many different stream IDs can be emitted by a single master device > coming into the SMMU. *That* is a property of the master, not the SMMU. >=20 > In the current arm,smmu binding I have a #stream-id-cells property in each > master. I can then feed that straight into of_parse_phandle_with_args to > enumerate the IDs for that master. The problem with that is we're > artificially restricted by MAX_PHANDLE_ARGS. Maybe I don't fully understand, but since we leave it up to the IOMMU binding to define the exact meaning of #iommu-cells, can't you simply use that to your advantage and define something like: iommus =3D <&smmu 0 7>; to mean IDs 0 to 7 for this particular IOMMU type? Thierry --T7mxYSe680VjQnyC Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJTjyGWAAoJEN0jrNd/PrOhJxsP/1QEAS+0iTQlOqf1sv4Oez0K DasrIeJ6Hg9a/Rgr3N+LLHF0uocLBhW17z+gG1wzPghsRyqzsnK9574Rlc+hpCEz 98+hbQq1Vv+gZJbm80kuSNZEwScteyNblaG7tSk83YQhqLs7EXczVuU9Mlg2TnCX z+bZArGke7KrMAseG4HcdoZiauMwM+2CcMXE8Nib43+OZj5Xpin8HHn9so53VZCc VSE+m+SVydcEVIq3DlEQOTNywCRHiyOtYy1esUPo+H9lkMOOFUkXnm0PYDP5iCFb TZ4NZ0AoJO6zjXSFRba9M1TpJEZ+ZXoEA8HxmRKXCUUZnoSpcnJc490T09K3cKLf bkdhqdwkGairvX849B9GaHWDFLy6v6ZBqYrFSC5xWh1J9SFDoq/7rpCosJxBmdOK EH6SSmPaQgtko3iFbSxU75BQoHLB+/TD/9xx5eWhmDTkfmV79Sg1cCo2sBrTZmvm J2m1Qmp1LKv7gwSq8dVQmhW+g19WyPKzr3GsqnZuaNpFvSPik61BloeNe9iTOLvS f1MHMWFhypILGZyhXmV7RCoMfl36L9eKAdgHY9oDZNBqGRgk7G19kCxxHA1lKbw/ /jiwG1IuFwme9QRODqgmfUJtYQcroGP6aQRQQ7ethVp9oxUH8AH5hHUFoB1P3mzO bu+xsmkOPv/NcGnNT1Ps =KYXF -----END PGP SIGNATURE----- --T7mxYSe680VjQnyC--