From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753160AbbCYQiD (ORCPT ); Wed, 25 Mar 2015 12:38:03 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:53293 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753087AbbCYQiA (ORCPT ); Wed, 25 Mar 2015 12:38:00 -0400 Date: Wed, 25 Mar 2015 09:37:03 -0700 From: Guenter Roeck To: Wolfram Sang Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters Message-ID: <20150325163703.GA8389@roeck-us.net> References: <20150212040126.GA1691@roeck-us.net> <20150216120951.GA2840@katana> <20150317042049.GA6765@roeck-us.net> <20150318132707.GD3580@katana> <550A4162.8000009@roeck-us.net> <20150319081612.GA900@katana> <20150319174314.GA17329@roeck-us.net> <20150319213937.GA899@katana> <5512C213.7030705@roeck-us.net> <20150325161504.GA29838@katana> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150325161504.GA29838@katana> User-Agent: Mutt/1.5.23 (2014-03-12) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A020201.5512E467.01E6,ss=1,re=0.001,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.001 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 3 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 25, 2015 at 05:15:04PM +0100, Wolfram Sang wrote: > Guenter, > > thanks for the update > > > Ultimately, the real problem is how i2c-dev accesses a client, not how > > i2c client drivers (who assume they have exclusive access to a chip) > > handle multi-command sequences. Forcing extensive locking on all drivers > > because of i2c-dev just doesn't seem to be the right thing to do. > > I agree. i2c-dev is too much of a special case. > > And since at24 has its own lock (I missed that), your patch might as > well be good enough to be applied, I'd think. > Ah, sorry, I blindly assumed that you are aware of that. Yes, at24 itself is not the problem, it is parallel access to the chip by i2c-dev. The same is actually true for all the other drivers I looked at; usually they have their own lock(s), but such locks do not protect against interference by i2c-dev. The bad part is that i2c-dev is heavily used by user space at my workplace, and that code happily messes with chips which are also handled by kernel drivers. But as I said, I have no real good idea how to fix that - neither the user-space code nor how i2c-dev interfers with (or completely messes up) device access by drivers. Thanks, Guenter From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: [PATCH] eeprom: at24: Add support for large EEPROMs connected to SMBus adapters Date: Wed, 25 Mar 2015 09:37:03 -0700 Message-ID: <20150325163703.GA8389@roeck-us.net> References: <20150212040126.GA1691@roeck-us.net> <20150216120951.GA2840@katana> <20150317042049.GA6765@roeck-us.net> <20150318132707.GD3580@katana> <550A4162.8000009@roeck-us.net> <20150319081612.GA900@katana> <20150319174314.GA17329@roeck-us.net> <20150319213937.GA899@katana> <5512C213.7030705@roeck-us.net> <20150325161504.GA29838@katana> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150325161504.GA29838@katana> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wolfram Sang Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On Wed, Mar 25, 2015 at 05:15:04PM +0100, Wolfram Sang wrote: > Guenter, > > thanks for the update > > > Ultimately, the real problem is how i2c-dev accesses a client, not how > > i2c client drivers (who assume they have exclusive access to a chip) > > handle multi-command sequences. Forcing extensive locking on all drivers > > because of i2c-dev just doesn't seem to be the right thing to do. > > I agree. i2c-dev is too much of a special case. > > And since at24 has its own lock (I missed that), your patch might as > well be good enough to be applied, I'd think. > Ah, sorry, I blindly assumed that you are aware of that. Yes, at24 itself is not the problem, it is parallel access to the chip by i2c-dev. The same is actually true for all the other drivers I looked at; usually they have their own lock(s), but such locks do not protect against interference by i2c-dev. The bad part is that i2c-dev is heavily used by user space at my workplace, and that code happily messes with chips which are also handled by kernel drivers. But as I said, I have no real good idea how to fix that - neither the user-space code nor how i2c-dev interfers with (or completely messes up) device access by drivers. Thanks, Guenter