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=-6.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 4C312C433E0 for ; Fri, 8 Jan 2021 08:41:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0038122248 for ; Fri, 8 Jan 2021 08:41:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725965AbhAHIlj (ORCPT ); Fri, 8 Jan 2021 03:41:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:60478 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725816AbhAHIli (ORCPT ); Fri, 8 Jan 2021 03:41:38 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E6873207C5; Fri, 8 Jan 2021 08:40:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610095258; bh=5RQMeUGl57mxmrnguXkd+pVtTieQ6mOXiWDV0BKtvgk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nubctBwA9jjzjEHNXuXUdtrvvYfvj8AR3LI3SU9qrdiu1PBM5xIsJYFzMj+YAphSy rRvs6IKtz/In63FZrEvEkryv6wwNbRiA6DUKu4yH+sRhbYevbP2Uw9pRBFixuw46TY eOPnDaWEhYvFCwDP4dDNQAOYTB2mrDqSDotpGmi1CrEeZA+gJFhlksgg8GM87Vhdxp LWz4W83SRXpchUaAs0QfeJlDjnOkceraFXAXX1ubwsuqULRt2rRtG5a7gtKswskQuD 4MUPXACG+j0z3V2YmBNcAWneOIeyNo6Vl8carmTUwtOLESkAzAc+QYYvwwCRthGPYe 6V3mpKkVuWXRA== Date: Fri, 8 Jan 2021 09:40:51 +0100 From: Wolfram Sang To: Marek Behun Cc: Russell King - ARM Linux admin , Andrew Lunn , netdev@vger.kernel.org, Pali =?utf-8?B?Um9ow6Fy?= , linux-i2c@vger.kernel.org Subject: Re: question about i2c_transfer() function (regarding mdio-i2c on RollBall SFPs) Message-ID: <20210108084051.GA1223@kunai> Mail-Followup-To: Wolfram Sang , Marek Behun , Russell King - ARM Linux admin , Andrew Lunn , netdev@vger.kernel.org, Pali =?utf-8?B?Um9ow6Fy?= , linux-i2c@vger.kernel.org References: <20210107192500.54d2d0f0@nic.cz> <20210107210248.GA894@kunai> <20210107224211.4f01c055@nic.cz> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="wac7ysb48OaltWcw" Content-Disposition: inline In-Reply-To: <20210107224211.4f01c055@nic.cz> Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org --wac7ysb48OaltWcw Content-Type: text/plain; charset=us-ascii Content-Disposition: inline > I thought as much, but maybe there is some driver which can offload > whole i2c_transfer to HW, and has to pass the addresses of the buffers > to the HW, and the HW can have problems if the buffers overlap > somewhere... Well, sure, you can never know what crazy HW is out there :) But that shouldn't prevent us from doing legit I2C transfers. The likeliness of such HW is low enough; They must process the whole transfer in one go (rare) AND have the limitiation with the buffer pointers (at least I don't know one) AND have no possibility of a fallback to a simpler mode where they can handle the transfer per message. If such a controller exists, it would need a new quirk flag, I'd say, and reject the transfer. But that shouldn't stop you from fixing your issue. Thanks for thinking thoroughly about drawbacks! Much appreciated. --wac7ysb48OaltWcw Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEOZGx6rniZ1Gk92RdFA3kzBSgKbYFAl/4Go8ACgkQFA3kzBSg KbZ/3RAAgpG2/2xH0qgj69NHKAWmrAt7x5TgdEMpjxJeD/ZKf7qAd0RY3q0bY9fF JpNrBbFerpnZ375i8o9ikRSXCvf2q+ZSWqp4L6esLRNZgL3YUQqg+q7KA2Zj+YTA BHBy11ncdVbKsb2X46hfuVAslfzTg6gDPs1kElNHtkIgGfw1eWlFPDi/svz72sl7 Btz5tZ04zRPUFaIMhVFvbJB03MH1wLhEOaC+ygG9OEQHoSs6THybZhi+G6sU1L09 gYrnvtdNqbHDp3An7NVVWLvhWS7JXRSbO1y5+eyB5W266+/wtCgwWlMOJxVgVShm nmdCNAb+XapPWPINJlXCyWdLWXRCc5Cw1oL0xt57b9WwNyDLS1xkwPDBhQl5FTjK 4GFaUDlkk8X4QzokUtcp+stT/X9VOFKpfs85iZLsAee6H3Td6G/W+hZ+NQcglHKD mY28kuTRlAR/pLNvD4CYSafjKhrALz/ELetpF7Y+GzcNODDqQxit3m7ZYRGZoQ06 gQhFsaXvkrTDfBYKu1Do5CIYNUvW7hW8TkIv9bIm85YfOJQw5pIOCmiPSmw+z0mF jt04pHInwp1VzCxFXkgdqWAz7ONI4uNoLHrSMb02P3tnooall1ZDbeGg8JSyeAqq 7WNVsJH5ONFSLOWM/y+SrRk5JpyJD2l0O9FV9BqxfYz8Ab1dpiM= =8etp -----END PGP SIGNATURE----- --wac7ysb48OaltWcw--