From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:57046 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750998AbcKQXk2 (ORCPT ); Thu, 17 Nov 2016 18:40:28 -0500 Date: Thu, 17 Nov 2016 15:40:24 -0800 From: Guenter Roeck To: Tom Levens Cc: Mike Looijmans , "jdelvare@suse.com" , "robh+dt@kernel.org" , "mark.rutland@arm.com" , "linux-kernel@vger.kernel.org" , "linux-hwmon@vger.kernel.org" , "devicetree@vger.kernel.org" Subject: Re: [PATCH v2 3/3] hwmon: ltc2990: support all measurement modes Message-ID: <20161117234024.GA26747@roeck-us.net> References: <1479384616-12479-1-git-send-email-tom.levens@cern.ch> <1479384616-12479-3-git-send-email-tom.levens@cern.ch> <410de6c9-a13e-51f7-4d66-6f4e2537c574@roeck-us.net> <582DEB81.6050806@topic.nl> <20161117185654.GA19338@roeck-us.net> <582E0A6C.5010307@topic.nl> <20161117215454.GA23571@roeck-us.net> <09DCF2E6-3F08-4F0E-837B-55F591008AAB@cern.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <09DCF2E6-3F08-4F0E-837B-55F591008AAB@cern.ch> Sender: linux-hwmon-owner@vger.kernel.org List-Id: linux-hwmon@vger.kernel.org On Thu, Nov 17, 2016 at 11:25:30PM +0000, Tom Levens wrote: > On 17 Nov 2016, at 22:54, Guenter Roeck wrote: > > On Thu, Nov 17, 2016 at 08:52:12PM +0100, Mike Looijmans wrote: > >> On 17-11-2016 19:56, Guenter Roeck wrote: > >>> On Thu, Nov 17, 2016 at 06:40:17PM +0100, Mike Looijmans wrote: > >>>> On 17-11-16 17:56, Guenter Roeck wrote: > >>>>> On 11/17/2016 04:10 AM, Tom Levens wrote: > >>>>>> Updated version of the ltc2990 driver which supports all measurement > >>>>>> modes available in the chip. The mode can be set through a devicetree > >>>>>> attribute. > >>>>> > >>> [ ... ] > >>> > >>>>>> > >>>>>> static int ltc2990_i2c_probe(struct i2c_client *i2c, > >>>>>> const struct i2c_device_id *id) > >>>>>> { > >>>>>> int ret; > >>>>>> struct device *hwmon_dev; > >>>>>> + struct ltc2990_data *data; > >>>>>> + struct device_node *of_node = i2c->dev.of_node; > >>>>>> > >>>>>> if (!i2c_check_functionality(i2c->adapter, > >>>>>> I2C_FUNC_SMBUS_BYTE_DATA | > >>>>>> I2C_FUNC_SMBUS_WORD_DATA)) > >>>>>> return -ENODEV; > >>>>>> > >>>>>> - /* Setup continuous mode, current monitor */ > >>>>>> + data = devm_kzalloc(&i2c->dev, sizeof(struct ltc2990_data), > >>>>>> GFP_KERNEL); > >>>>>> + if (unlikely(!data)) > >>>>>> + return -ENOMEM; > >>>>>> + data->i2c = i2c; > >>>>>> + > >>>>>> + if (!of_node || of_property_read_u32(of_node, "lltc,mode", > >>>>>> &data->mode)) > >>>>>> + data->mode = LTC2990_CONTROL_MODE_DEFAULT; > >>>>> > >>>>> Iam arguing with myself if we should still do this or if we should read > >>>>> the mode > >>>>> from the chip instead if it isn't provided (after all, it may have been > >>>>> initialized > >>>>> by the BIOS/ROMMON). > >>>> > >>>> I think the mode should be explicitly set, without default. There's no way > >>>> to tell whether the BIOS or bootloader has really set it up or whether the > >>>> chip is just reporting whatever it happened to default to. And given the > >>>> chip's function, it's unlikely a bootloader would want to initialize it. > >>>> > >>> Unlikely but possible. Even if we all agree that the chip should be configured > >>> by the driver, I don't like imposing that view on everyone else. > >>> > >>>> My advice would be to make it a required property. If not set, display an > >>>> error and bail out. > >>>> > >>> It is not that easy, unfortunately. It also has to work on a non-devicetree > >>> system. I would not object to making the property mandatory, but we would > >>> still need to provide non-DT support. > >>> > >>> My "use case" for taking the current mode from the chip if not specified > >>> is that it would enable me to run a module test with all modes. I consider > >>> this extremely valuable. > >> > >> Good point. > >> > >> The chip defaults to measuring internal temperature only, and the mode > >> defaults to "0". > >> > >> Choosing a mode that doesn't match the actual circuitry could be bad for the > >> chip or the board (though unlikely, it'll probably just be useless) since it > >> will actively drive some of the inputs in the temperature modes (which is > >> default for V3/V4 pins). > >> > >> Instead of failing, one could choose to set the default mode to "7", which > >> just measures the 4 voltages, which would be a harmless mode in all cases. > >> > >> As a way to let a bootloader set things up, I think it would be a good check > >> to see if CONTROL register bits 4:3 are set. If "00", the chip is not > >> acquiring data at all, and probably needs configuration still. In that case, > >> the mode must be provided by the devicetree (or the default "7"). > >> If bits 4:3 are "11", it has already been set up to measure its inputs, and > >> it's okay to continue doing just that and use the current value of 2:0 > >> register as default mode (if the devicetree didn't specify any mode at all). > >> > > > > At first glance, agreed, though by default b[3:4] are 00, and only the > > internal temperature is measured. Actually, the 5 mode bits are all > > relevant to determine what is measured. Maybe it would be better to take > > all 5 bits into account instead of blindly setting b[34]:=11 and a specific > > setting of b[0:2]. Sure, that would make the mode table a bit larger, > > but then ltc2990_attrs_ena[] could be made an u16 array, and a table size > > of 64 bytes would not be that bad. > > I would tend to agree that it should be possible to configure all 5 mode > bits through the devicetree. What I would propose is as follows. > > If a devicetree node exists, the mode parameter(s?) are required and the > chip is initialised. > > If a devicetree node doesn't exist, it is assumed that the chip has > already been configured (by the BIOS, etc). The mode is read from the > chip to set the visibility of the sysfs attributes. In the worst case, where the > chip has not been configured by another source, it would only be possible > to measure the internal temperature -- but I think this is an acceptable > limitation. > SGTM. > The only case that this does not cover is if the device tree node > exists but the chip is expected to be configured by some other source. > Maybe I am wrong, but I would not expect this to be a terribly common > situation. > > What do you think? > I would not bother about this case. Just make the mode property mandatory. Thanks, Guenter