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: Fri, 27 Mar 2015 08:42:02 -0700 Message-ID: <55157A4A.1090305@roeck-us.net> References: <20150318132707.GD3580@katana> <550A4162.8000009@roeck-us.net> <20150319081612.GA900@katana> <20150319174314.GA17329@roeck-us.net> <20150319213937.GA899@katana> <5512C213.7030705@roeck-us.net> <20150327080947.GA900@katana> <5515523F.9010609@roeck-us.net> <20150327130108.GA19151@katana> <551557B4.5000504@roeck-us.net> <20150327152727.GA27238@katana> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150327152727.GA27238@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 03/27/2015 08:27 AM, Wolfram Sang wrote: > On Fri, Mar 27, 2015 at 06:14:28AM -0700, Guenter Roeck wrote: >> On 03/27/2015 06:01 AM, Wolfram Sang wrote: >>> On Fri, Mar 27, 2015 at 05:51:11AM -0700, Guenter Roeck wrote: >>>> On 03/27/2015 01:09 AM, Wolfram Sang wrote: >>>>> >>>>>> just to give you an update: I do have some code, but it is a bit messy, >>>>>> and it doesn't work well for ds2482 (the chip behind it still hangs up >>>>>> if I access it in parallel through i2c-dev). On top of that, it causes >>>>>> pretty significant slow-downs when accessing other devices on the same >>>>>> bus at the same time. Not surprising, I guess, since it expands the scope >>>>>> of the bus lock significantly. >>>>> >>>>> Just to get a better idea: Did you try taking the adapter_lock before >>>>> the two SMBus command which needed to be concatenated (and use >>>>> smbus_xfer directly)? >>>>> >>>> I did. I didn't use smbus_xfer directly, though, but introduced lockless >>>> versions of the various smbus commands, and kept using those. >>> >>> And then the chip still hangs? Or was that the performance penalty here? >>> >> Parallel access to a second eeprom chip on the same bus was much slower >> than before. > > Interesting. I wonder what is the reason, I would have expected just a > small delay. Would you mind sending the patches for the non-locked smbus > routines? Would be nice to have that around in case I or someone else > find some time to try as well. > I pushed it into my linux repository at github (https://github.com/groeck/linux, branch at24). >> Also, the new code did not solve the problem for ds2482 (completely unrelated >> to the at24 driver of course). Even with proper locking, the chip ended up >> hanging after some parallel accesses through i2c-dev. Granted, ds2482 is >> a difficult beast, but it is still annoying how access through i2c-dev >> can mess it up. > > I assume you basically replaced the access_lock with the adapter_lock > with this one? > yes. >> >> The latter is what bothered me more: What is the point of all this if we >> still can not ensure correct operation ? > > Yeah, this is not good at all. > > How do you use i2c-dev BTW? i2c_rdwr_msgs? What about iterating over all > msgs in that and check for busy addresses? > In this case, I just used i2cdump from one session while accessing the chip from another session using the driver. Guenter