From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932303AbaD3FJE (ORCPT ); Wed, 30 Apr 2014 01:09:04 -0400 Received: from mail-bl2lp0208.outbound.protection.outlook.com ([207.46.163.208]:49469 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750965AbaD3FJC convert rfc822-to-8bit (ORCPT ); Wed, 30 Apr 2014 01:09:02 -0400 From: "Li.Xiubo@freescale.com" To: Mark Rutland CC: "broonie@kernel.org" , "rob@landley.net" , "robh+dt@kernel.org" , Pawel Moll , "ijc+devicetree@hellion.org.uk" , "galak@codeaurora.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCHv2 1/3] dt/bindings: Add the DT binding documentation for endianness Thread-Topic: [PATCHv2 1/3] dt/bindings: Add the DT binding documentation for endianness Thread-Index: AQHPXsXw941G9fcOpUWOzogqfmIRtJse4A8AgArGTqA= Date: Wed, 30 Apr 2014 05:08:46 +0000 Message-ID: References: <1398235595-13370-1-git-send-email-Li.Xiubo@freescale.com> <1398235595-13370-2-git-send-email-Li.Xiubo@freescale.com> <20140423083412.GA30036@e106331-lin.cambridge.arm.com> In-Reply-To: <20140423083412.GA30036@e106331-lin.cambridge.arm.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [123.151.195.49] x-forefront-prvs: 0197AFBD92 x-forefront-antispam-report: SFV:NSPM;SFS:(10009001)(6009001)(428001)(199002)(189002)(51704005)(164054003)(80022001)(74662001)(76482001)(83322001)(66066001)(92566001)(76576001)(20776003)(4396001)(81542001)(85852003)(19580395003)(81342001)(2656002)(74502001)(31966008)(80976001)(86362001)(54356999)(99396002)(19580405001)(77982001)(46102001)(87936001)(50986999)(99286001)(79102001)(101416001)(74316001)(76176999)(77096999)(33646001)(83072002)(24736002);DIR:OUT;SFP:1101;SCL:1;SRVR:BY2PR03MB507;H:BY2PR03MB505.namprd03.prod.outlook.com;FPR:DCD8F4FF.A0D21425.40F19932.8AE8C201.202E0;MLV:sfv;PTR:InfoNoRecords;A:1;MX:1;LANG:en; Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-OriginatorOrg: freescale.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > diff --git a/Documentation/devicetree/bindings/endianness/endianness.txt > b/Documentation/devicetree/bindings/endianness/endianness.txt > > new file mode 100644 > > index 0000000..64f1d5e > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/endianness/endianness.txt > > @@ -0,0 +1,55 @@ > > +Device-Tree binding for device endianness > > + > > +The endianness mode of CPU & Device scenarios: > > + Index CPU Device > > + ------------------------ > > + 1 LE LE > > + 2 LE BE > > + 3 BE BE > > + 4 BE LE > > + > > +For one device driver, which will run in different scenarios above > > +on different SoCs using the devicetree, we need one way to simplify > > +this. > > + > > +Required properties: > > +- [prefix]-endian: this is one string property and must be one > > + of 'be', 'le' and 'native' if it is present. > > What exactly is the prefix? > > This file name and file heading implies this is a common endianness > binding, which it is not. There are many existing bindings that have > mechanisms for describing the endianness of components, and they have > settled on a different pattern. > > We already have many bindings with {big,little}-endian{,-*} boolean > properties. It would be better to take that common case and document > that as the standard way of doing things rather than inventing a > completely different mechanism. > Well, yes, I'll follow your advice. > > +The endianness mode: > > + 'le' : device is in little endian mode, > > + 'be' : device is in big endian mode, > > + 'native' : device is in the same endian mode with the CPU. > > What exactly do you mean by native? A device which always matches the > endianness of the CPU even if it changes? How common is that? > It's originally based the regmap, and the 'native' is make no sense here, I'll reconstruct this. > > + > > +Examples: > > +Scenario 1 : CPU in LE mode & device in LE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'native'; > > +}; > > If the device is LE, then surely we should describe the device as LE. > The kernel knows what endianness it is, might choose to change the CPU > endianness, but regardless can do the right thing. Telling it a device > is native is useless unless the device changes endianness with the CPU. > Yes, you are right. > > + > > +Scenario 2 : CPU in LE mode & device in BE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'be'; > > +}; > > + > > +Scenario 3 : CPU in BE mode & device in BE mode. > > +dev: dev@40031000 { > > + compatible = "name"; > > + reg = <0x40031000 0x1000>; > > + ... > > + [prefix]-endian = 'native'; > > +}; > > Likewise. > > Thanks, > Mark. >