From owner-svn-src-head@freebsd.org Tue Oct 10 16:42:35 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 6C7B2E36FD2 for ; Tue, 10 Oct 2017 16:42:35 +0000 (UTC) (envelope-from ian@freebsd.org) Received: from outbound1a.eu.mailhop.org (outbound1a.eu.mailhop.org [52.58.109.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 09B73638AC for ; Tue, 10 Oct 2017 16:42:34 +0000 (UTC) (envelope-from ian@freebsd.org) X-MHO-User: 01450651-adda-11e7-a893-25625093991c X-Report-Abuse-To: https://support.duocircle.com/support/solutions/articles/5000540958-duocircle-standard-smtp-abuse-information X-Originating-IP: 73.78.92.27 X-Mail-Handler: DuoCircle Outbound SMTP Received: from ilsoft.org (unknown [73.78.92.27]) by outbound1.eu.mailhop.org (Halon) with ESMTPSA id 01450651-adda-11e7-a893-25625093991c; Tue, 10 Oct 2017 16:42:30 +0000 (UTC) Received: from rev (rev [172.22.42.240]) by ilsoft.org (8.15.2/8.15.2) with ESMTP id v9AGgQnd004242; Tue, 10 Oct 2017 10:42:26 -0600 (MDT) (envelope-from ian@freebsd.org) Message-ID: <1507653746.84167.40.camel@freebsd.org> Subject: Re: svn commit: r323465 - head/usr.sbin/i2c From: Ian Lepore To: Andriy Gapon , src-committers@FreeBSD.org, svn-src-all@FreeBSD.org, svn-src-head@FreeBSD.org Date: Tue, 10 Oct 2017 10:42:26 -0600 In-Reply-To: References: <201709112149.v8BLncAs049328@repo.freebsd.org> <4c4a916f-9960-6d7f-3389-37b998ba980b@FreeBSD.org> <1507651963.84167.37.camel@freebsd.org> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.18.5.1 FreeBSD GNOME Team Port Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 10 Oct 2017 16:42:35 -0000 On Tue, 2017-10-10 at 19:20 +0300, Andriy Gapon wrote: > On 10/10/2017 19:12, Ian Lepore wrote: > > > > i2c -s is not a thing that's done routinely in a production system or > > normal system operations... it's something a person does manually when > > trying to configure or debug a system.  In that situation, there is > > more harm in being told there are no working devices on the bus when in > > fact everything is fine, than there is some some hypothetical device > > doing some hypothetical "bad thing" in response to a read command.  In > > all my years of working with i2c stuff I've never seen a device doing > > anything more harmful than hanging the bus, requiring a reset (and even > > causing that requires worse behavior than an unexpected read).  On the > > other hand, I've seen a lot of people frustrated that i2c -s on freebsd > > says there are no devices, while the equivelent command on linux shows > > that everything is fine. > Okay. > > However, I will just mention that in the past I used to own a system where > scanning the bus would make a slave that controlled CPU frequency to change it > to some garbage.  The system "just" crashed, but theoretically the damage could > have been worse. > Also, I own a system right now where scanning the bus results in something like > what you mentioned, but a little bit worse, the hanging bus that can be brought > back only by a power cycle (not even a warm reset). > These systems didn't used to hang on i2c -s, and now they do? -- Ian