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