Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753491AbbEMH21 (ORCPT ); Wed, 13 May 2015 03:28:27 -0400 Received: from smtp-out-159.synserver.de ([212.40.185.159]:1100 "EHLO smtp-out-159.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752051AbbEMH2Y (ORCPT ); Wed, 13 May 2015 03:28:24 -0400 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 29955 Message-ID: <5552FD16.9050306@metafoo.de> Date: Wed, 13 May 2015 09:28:22 +0200 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Jonathan Cameron , Robert Dolca , linux-iio@vger.kernel.org CC: linux-kernel@vger.kernel.org, Hartmut Knaack , Peter Meerwald , Denis CIOCCA Subject: Re: [PATCH RFC 1/3] iio: Add symlink to triggers in the device's trigger folder References: <1429174868-11953-1-git-send-email-robert.dolca@intel.com> <1429174868-11953-2-git-send-email-robert.dolca@intel.com> <554CD236.4000404@kernel.org> <555230B0.3050700@metafoo.de> <55524F4C.90604@kernel.org> In-Reply-To: <55524F4C.90604@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3372 Lines: 67 On 05/12/2015 09:06 PM, Jonathan Cameron wrote: > On 12/05/15 17:56, Lars-Peter Clausen wrote: >> On 05/08/2015 05:11 PM, Jonathan Cameron wrote: >>> On 16/04/15 05:01, Robert Dolca wrote: >>>> This patch adds a new function called iio_trigger_register_with_dev >>>> which is a wrapper for iio_trigger_register. Besides the iio_trigger >>>> struct this function requires iio_dev struct. It adds the trigger in >>>> the device's trigger list and saves a reference to the device in the >>>> trigger's struct. >>>> >>>> When the device is registered, in the trigger folder of the device >>>> (where current_trigger file resides) a symlink is being created for >>>> each trigger that was registered width iio_trigger_register_with_dev. >>>> >>>> # ls -l /sys/bus/iio/devices/iio:device0/trigger/ >>>> total 0 >>>> -rw-r--r-- 1 root root 4096 Apr 16 08:33 current_trigger >>>> lrwxrwxrwx 1 root root 0 Apr 16 08:33 trigger0 -> ../../trigg >>>> er0 >>>> >>>> This should be used for device specific triggers. Doing this the user space >>>> applications can figure out what if the trigger registered by a specific device >>>> and what should they write in the current_trigger file. Currently some >>>> applications rely on the trigger name and this does not always work. >>>> >>>> This implementation assumes that the trigger is registered before the device is >>>> registered. If the order is not this the symlink will not be created but >>>> everything else will work as before. >>>> >>>> Signed-off-by: Robert Dolca >>> I was rather hoping we'd get a few more comments on this. >>> In principle I like the idea, but it's new ABI and does make life >>> a tiny bit more complex, so what do people think? >>> >>> Few trivial code comments inline. >> >> I don't think it adds more information. Both the trigger and the >> device get registered for the same parent device, so you can already >> easily find the trigger for a device by going to the parent device >> and taking a look at the triggers registered by the parent device. > I had the same thought. The question is whether the slightly gain in > simplicity for userspace is worth it... I'm undecided at the moment. As you may have guessed by now I'm always quite conservative when it comes to introducing new ABI. Simply because we have to maintain it forever, the less stuff to maintain forever the better. Hence I think all new ABI needs a compelling reason, e.g. like a improvement in performance. And of course this patch slightly simplifies things, but in my opinion not enough to justify a ABI extension. We can always find ways to simplify the interface, but the metric for ABI should be whether the simplification actually matters. In this case I don't think it does, finding the trigger for a device is not really hot-path. The amount of time saved will be disappear in the noise. And in my opinion applications shouldn't directly use the low-level ABI but rather use middle-ware libraries/frameworks, like e.g. libiio, and that's where you'd hide the complexities of a operation. - Lars -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/