From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6127DC282DD for ; Wed, 8 Jan 2020 13:19:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40B9C20643 for ; Wed, 8 Jan 2020 13:19:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727472AbgAHNTc (ORCPT ); Wed, 8 Jan 2020 08:19:32 -0500 Received: from sauhun.de ([88.99.104.3]:34940 "EHLO pokefinder.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726087AbgAHNTc (ORCPT ); Wed, 8 Jan 2020 08:19:32 -0500 Received: from localhost (p54B332C6.dip0.t-ipconnect.de [84.179.50.198]) by pokefinder.org (Postfix) with ESMTPSA id 9DACA2C05CE; Wed, 8 Jan 2020 14:19:29 +0100 (CET) Date: Wed, 8 Jan 2020 14:19:29 +0100 From: Wolfram Sang To: Laurent Pinchart Cc: Luca Ceresoli , Wolfram Sang , linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Kieran Bingham , Jacopo Mondi , Vladimir Zapolskiy Subject: Re: [RFC PATCH 3/5] i2c: core: add function to request an alias Message-ID: <20200108131929.GA834@kunai> References: <20191231161400.1688-1-wsa+renesas@sang-engineering.com> <20191231161400.1688-4-wsa+renesas@sang-engineering.com> <20200101165515.GC6226@pendragon.ideasonboard.com> <20200102211327.GB1030@kunai> <20200103001056.GJ4843@pendragon.ideasonboard.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="SLDf9lqlvOQaIe6s" Content-Disposition: inline In-Reply-To: <20200103001056.GJ4843@pendragon.ideasonboard.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org --SLDf9lqlvOQaIe6s Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable > > > As I said to Laurent, too, I think the risk that a bus is not fully > > > described is higher than a device which does not respond to a read_by= te. > > > In both cases, we would wrongly use an address in use. >=20 > I don't fully agree with this, I think we shouldn't impose a penalty on > every user because some device trees don't fully describe the hardware. I haven't decided yet. However, my general preference is that for a generic OS like Linux, saftey comes first, then performance. If you have a fully described DT, then the overhead will be 1 read_byte transaction per requested alias at probe time. We could talk about using quick_read to half the overhead. You could even patch it away, if it is too much for $customer. > I think we should, at the very least, skip the probe and rely on DT if > DT explicitly states that all used addresses are listed. We discussed a > property to report addresses used by devices not described in DT, if > that property is listed I would prefer trusting DT. Yeah, we discussed this property and I have no intentions of dropping it. I haven't though of including it into this series, but it probably makes sense. We don't have to define much anyhow, just state what already exists, I guess. =46rom Documentation/devicetree/bindings/i2c/i2c-ocores.txt: dummy@60 { compatible =3D "dummy"; reg =3D <0x60>; }; I think "dummy" is generic enough to be described in i2c.txt. --SLDf9lqlvOQaIe6s Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEOZGx6rniZ1Gk92RdFA3kzBSgKbYFAl4V1twACgkQFA3kzBSg KbbzSRAAiuALUdJOg3tKldF65q6HmHIJ6tCA7sLUgy3dPEw0kyKedtbIRFpiWDox 7bjYE3i6uOVxY2OLmLar8JKhnUHJUUjuVKkE7XLMMUtnt6cx/mlHdB77NGC/2sB0 WacCezXiESG4ZbKdRWhBW77/qpqbUgU6MJ9J1+I9oAWnvqGjVZyPLug09koutHZH JJUa90lVok00aoWva8I6ZAG3b2zmyhi62u4gr+JIet4JptOhzwBIW3jYKvWZkDHe +TGFxC2tnoXzhDfW8cRrrKgacZ4dOvRtLh4FtDokqTThX/MyNssL/JPn7jrMeYbZ 7sCy1u9AAo/QaU6+UsqyIEdVoG4vNGN9AbHeJHT+z8OfKAN9xpEcra+GLz3cDXC3 id+swyMCbe9iHADkLS3/d5E+7RX2OJARiKL3yff7DC/7KFMLHMpAlXewuigrt+uG cxRw372i8GZT7nIl4g9reufXwLoSwXRi6hYpEHr8sov72um0SKmY68HGgrjOlnMM tsrmZQOmSk4FhXJrsX6tXo8D/ExRty/w/g3n+KApzsNpAhLaeRlDr81lZPD76Jfw BqSdcyvfOjAKJNb9ag3N+GIXUldeNIZE0HPwV6SZtcUPlbdOy7I8F4qKIiS6ni/N bpp42rEZdntGbT2hA4GRgcIHdbprlSHlwgaPxjoD10BaLbtXJjM= =NLtL -----END PGP SIGNATURE----- --SLDf9lqlvOQaIe6s--