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[209.132.180.67]) by mx.google.com with ESMTP id 1si14434222plo.265.2019.09.03.02.10.51; Tue, 03 Sep 2019 02:11:07 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728188AbfICJJ7 (ORCPT + 99 others); Tue, 3 Sep 2019 05:09:59 -0400 Received: from hostingweb31-40.netsons.net ([89.40.174.40]:43345 "EHLO hostingweb31-40.netsons.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726631AbfICJJ7 (ORCPT ); Tue, 3 Sep 2019 05:09:59 -0400 Received: from [109.168.11.45] (port=41976 helo=[192.168.101.73]) by hostingweb31.netsons.net with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.92) (envelope-from ) id 1i54p2-002t5L-6Q; Tue, 03 Sep 2019 11:09:56 +0200 Subject: Re: [RFC,v2 3/6] media: dt-bindings: add DS90UB954-Q1 video deserializer To: Wolfram Sang Cc: linux-media@vger.kernel.org, linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Mauro Carvalho Chehab , Rob Herring , Mark Rutland , Sakari Ailus , Hans Verkuil , Laurent Pinchart , Kieran Bingham , Jacopo Mondi , Vladimir Zapolskiy , Peter Rosin References: <20190723203723.11730-1-luca@lucaceresoli.net> <20190723203723.11730-4-luca@lucaceresoli.net> <20190902204841.GB7253@kunai> From: Luca Ceresoli Message-ID: <63d99d6d-ecdd-7dd8-0dcb-126bfd89b258@lucaceresoli.net> Date: Tue, 3 Sep 2019 11:09:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190902204841.GB7253@kunai> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - hostingweb31.netsons.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lucaceresoli.net X-Get-Message-Sender-Via: hostingweb31.netsons.net: authenticated_id: luca+lucaceresoli.net/only user confirmed/virtual account not confirmed X-Authenticated-Sender: hostingweb31.netsons.net: luca@lucaceresoli.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Wolfram, On 02/09/19 22:48, Wolfram Sang wrote: > >> + - i2c-alias-pool: list of I2C addresses that are known to be available on the >> + "local" (SoC-to-deser) I2C bus; they will be picked at >> + runtime and used as aliases to reach remove I2C chips > > After some internal discussion, I have been kinda convinced that it may > be better to assume all non-described addresses are free to use and > enter the pool. > > The problem with the binding above is that you may run out of aliases > depending on how many aliases one to-be-attached module needs or how > many modules will be attached. Not if you define enough addresses in the pool. E.g. the DS90UB954 hardware can have 8 aliases per port, so if you have (n_ports * 8) addresses in the pool the problem is solved. > And another add-on module with > non-repogrammable devices may occupy addresses from the defined pool > above. You mean a new device on the local (SoC-to-ATR) bus? Well, it could as well occupy a non-described address that the ATR has already picked as an alias. > I am not perfectly happy with the assumption that all undescribed > addresses are automatically free. That also might need DTS updates to > describe all clients properly. But this change only needs to be done > once, and it will improve the description of the hardware. Right, but I still suspect some users won't do their homework and discover address conflicts at runtime, maybe months later, in a painful way. Also a chip might be undocumented on a given board, so they could do their homework and still have problems. Despite my comments, I'm not strongly against your proposal. To me it doesn't seem to solve any problem, while it does introduce some degree of risk. Could you elaborate more on but what benefit it introduces? Thanks, -- Luca