From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from down.free-electrons.com ([37.187.137.238]:33624 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752820AbcGSGza (ORCPT ); Tue, 19 Jul 2016 02:55:30 -0400 Subject: Re: [PATCH v2 4/4] hwmon: iio: add label for channels read by iio_hwmon To: Jonathan Cameron , jdelvare@suse.com, linux@roeck-us.net, knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net, maxime.ripard@free-electrons.com, wens@csie.org, lee.jones@linaro.org References: <1468576754-3273-1-git-send-email-quentin.schulz@free-electrons.com> <1468576754-3273-5-git-send-email-quentin.schulz@free-electrons.com> Cc: linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-iio@vger.kernel.org, linux-arm-kernel@lists.infradead.org, thomas.petazzoni@free-electrons.com, antoine.tenart@free-electrons.com From: Quentin Schulz Message-ID: <578DCED5.6080408@free-electrons.com> Date: Tue, 19 Jul 2016 08:55:17 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-hwmon-owner@vger.kernel.org List-Id: linux-hwmon@vger.kernel.org On 18/07/2016 14:24, Jonathan Cameron wrote: > On 15/07/16 10:59, Quentin Schulz wrote: >> Currently, iio_hwmon only exposes values of the IIO channels it can read >> but no label by channel is exposed. >> >> This adds exposition of sysfs files containing label for IIO channels it >> can read based on extended_name field of the iio_chan_spec of the channel. >> If the extended_name field is empty, the sysfs file is not created by >> iio_hwmon. > Hmm. This is not the intent of extended name at all. That exists to add > a small amount of information to an constructed IIO channel name. > Typically it's used to indicate physically wired stuff like: > > in_voltage0_vdd_raw for cases where that channel of the ADC is hard wired > to the vdd. In this particular case the use might actually work as the > vdd makes it clear it's a voltage - in general that's not the case. > > Use of extended_name at all in IIO is only done after extensive review. > It adds nasty custom ABI to a device, so the gain has to be considerable > to use it. > > When I read your original suggestion of adding labels, I was expecting the > use of datasheet_name. That has the advantage of being well defined by > the datasheet (if not it should not be provided) + not being used in > the construction of the IIO channel related attributes. However, that > may still not correspond well to the expected labelling in hwmon. Good to know for extend_name use cases. While doing further testing, I noticed the extend_name is also appended to the sysfs filename.. which is definitely not what we want. I've checked for datasheet_name and it is only used to be compared to adc_channel_label from iio_map structure. Same for adc_channel_label (which has to be the same as datasheet_name of the iio_chan_spec it is linked to). So I could use this instead of extend_name to put a label on a channel. However, I thought of it to be more a way to identify the hardware in the datasheet more than giving users a hint on what it is. That's what "git grep adc_channel_label" told me. It's definitely better to use datasheet_name over extend_name for channel labeling but I don't know if it's really the good variable to use for labeling? In my understanding of datasheet_name, in my case it would be more "temp_gpadc" than "SoC temperature", that's what I mean. > Thinking more on this, the label is going to often be a function of how > the board is wired up... Perhaps it should be a characteristic of the > channel_map (hence from DT or similar) rather than part of the IIO driver > itself? Hmm.. I would not put a property in the DT only for labeling. [...]