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Tue, 16 Jun 2026 10:27:10 -0700 (PDT) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 16 Jun 2026 12:26:58 -0500 Message-Id: From: "Kurt Borja" To: "David Lechner" , "Kurt Borja" , "Jonathan Cameron" , =?utf-8?q?Nuno_S=C3=A1?= , "Andy Shevchenko" , "Rob Herring" , "Krzysztof Kozlowski" , "Conor Dooley" Cc: "Nguyen Minh Tien" , , , Subject: Re: [PATCH 0/4] iio: adc: new ti-ads112c14 driver X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <20260615-iio-adc-ti-ads122c14-v1-0-e6bdadf7cb2b@baylibre.com> In-Reply-To: On Tue Jun 16, 2026 at 10:21 AM -05, David Lechner wrote: > On 6/15/26 7:18 PM, Kurt Borja wrote: >> Hi David, >>=20 >> On Mon Jun 15, 2026 at 4:59 PM -05, David Lechner (TI) wrote: >>> This adds support for TI ADS112C14 and ADS122C14 ADC chips. >>> >>> The closest thing we've seen to this in the kernel already is ads124s08= . >>> However, that has a completely different register map and the DT >>> bindings are incomplete and the driver is extremely basic. So I've just >>> started from scratch here. >>> >>> We've also had a similar submission recently for ADS1220 [1]. That chip >>> is in a similar situation to ads124s08 in that it has a different >>> register map (but the submitted DT bindings are better than the ones fo= r >>> ads124s08, even if still a bit incomplete). And literally as I was >>> writing the previous sentence, another series [2] was sent for yet >>> another similar family of chips (ADS1262). That one is even more comple= x >>> in the feature set than the ones I am working on. I was going to polish >>> up the driver a bit more before submitting it, but now it seems more >>> urgent to coordinate with the other two series to align on how we would >>> like to handle all of these. >>> >>> [1]: https://lore.kernel.org/linux-iio/20260610151342.44274-1-zizuzacke= r@gmail.com/ >>> [2]: https://lore.kernel.org/linux-iio/20260612-ads126x-v1-0-894c788d03= ed@gmail.com/ >>> >>> All of these chips have in common that they are designed for use with >>> RTDs and thermocouples and so they look very similar to each other in >>> terms of wiring and feature set, even if the register maps are >>> different. They are in the gray area where we could either keep them >>> separate because they are just different enough, or we could do like >>> we've done before with ad_sigma_delta and have a bit of an abstraction >>> layer for the register differences and otherwise try to share as much >>> code as possible. Normally, I would lean towards keeping them separate, >>> but in this case, I'm considering trying to share code because the >>> devicetree bindings for the inputs is complex and is going to be mostly >>> the same across all of these chips. >>=20 >> The channel configuration is indeed very similar for the three chips. >> All three have IDAC, BOC and VREF configurations. > > Hmm... I forgot to include the burnout current in the DT bindings. Follow= ing > the channel =3D "conditions for measurement" pattern that I have set out = here > I guess that would mean that we would need to have the same inputs twice > when using the burnout. One "channel" would be the one used to do a "prec= ision" > measurement and the other would be the one to do open/short circuit detec= tion. > > > i2c { > #address-cells =3D <1>; > #size-cells =3D <0>; > > adc@40 { > compatible =3D "ti,ads112c14"; > reg =3D <0x40>; > > avdd-supply =3D <&avdd>; > dvdd-supply =3D <&dvdd>; > > refp-supply =3D <&avdd>; > > #address-cells =3D <1>; > #size-cells =3D <0>; > > channel@0 { > reg =3D <0>; > diff-channels =3D <1>, <2>; > excitation-channels =3D <0>, <3>; > excitation-current-microamp =3D <500>; > current-chopping; > ti,vref-source =3D ; > label =3D "rtd-precision"; > }; > > channel@1 { > reg =3D <0>; > diff-channels =3D <1>, <2>; > excitation-channels =3D <0>, <3>; > excitation-current-microamp =3D <500>; > burnout-current-nanoamp =3D <1000>; > ti,vref-source =3D ; > label =3D "rtd-diagnostic"; > }; This would mean we wouldn't be able to use iio_chan_spec .channel and .channel2 to describe inputs because of duplicate sysfs attributes, no? > }; > }; > >>=20 >>> >>> If we decide to go the route of sharing code, we could still merge this >>> series as-is and then do the refactoring to add the abstraction layer i= n >>> a follow-up series that also adds support for the first of the other >>> chips. >>=20 >> Do you have a proposal of how such an abstraction would look like? I do >> like the idea of abstracting the firmware parsing, scales and shared >> calculations. > > As mentioned, it would look a bit like the ad_sigma_delta ADC driver. > Basically, each chip (family with same registers) would still have it's > own driver that include the chip-specific const info structs. In this > case, these would also include function pointers for all of the functions > that need to access registers. And there will be lots of supports_... boo= l > flags for the shared code to use. > >>=20 >>> >>> This series includes just basic support for reading single measurements >>> from the ADC and gain selection via the scale attribute. I plan to >>> follow this up with additional series to add support for buffered reads= , >>> filtering/oversampling configuration, event support, gpio controller >>> support and perhaps a few other things that are slipping my mind right >>> now. >>> >>> The most interesting part about this (that I alluded to above) is the >>> way channels are handled. These are multipling ADCs with differential >>> and single-ended inputs. But what sets them apart from other similar >>> chips is that since they are designed for use with RTDs, there can also >>> be a current output required to excite the RTD and this current output >>> might be different for different channels. So the way I conceptualized >>> the channels is that the devicetree specifies the conditions needed >>> to take a particular measurement rather than being purely a physical >>> channel. >>> >>> This makes things more flexible, but does make the driver a bit more >>> complex. For example, knowing when the current output needs to be >>> enabled or disabled. For now, I have chosen a lazy-enable where they >>> are not turned on until the first measurement is taken that requires >>> them, but then they stay on until another measurement is taken that >>> doesn't require them. This can lead to some oddness with the diagnostic >>> channels that may be measuring something that indirectly requires the >>> current output (i.e. the external reference voltage when it is connecte= d >>> to a resistor rather than a power supply). This means you need to take >>> a measurement that requires the current output to be enabled before the >>> diagnostic channels will give accurate readings. >>=20 >> This is the same approach I took around the BOC, it feels kinda hacky >> but it makes sense. Just an idea I thought about just now: What if we >> have an additional write-only "_enable" sysfs attribute for these >> channels? > > I would not want to make a write-only attribute, we always want to be > able to read back what the current state is. Yeah, I don't know why I said WO. Reading would be fine too. > > Do you mean an _enable for just the BOC? I think I would do it like I > suggested above instead. No, no just the BOC. The BOC, IDAC and rest of side effects. Thinking about it some more, it would be a bit redundant but clearer if proper documentation is provided. > >>=20 >> The approach I took for the IDAC was to have a single configuration that >> it's enabled for all channels. This makes some sense in my device when >> thinking about optimal software sequencial reads, because of the >> register layout, but I also see the value in having per-channel IDAC >> configuration. I think I will take your approach, so we have the same >> channel configuration around this. > > There are only two IDACs but on chips with 8 AIN pins we could have two > RTDs wired up and if both require 2 IDACs, then we can't have a fixed > setting for the IDACs. This is why I made it per-channel. I'll make it per-channel too. > >>=20 >> Have you thought about how to implement the BOC? In the ADS1262 the >> feature can be found "Sensor Bias". What I did was add per channel DT >> properties for this too. > > See above. > >>=20 >> Another question. When you implement power management in the future, >> will you enable autosuspend? IDAC currents will be lost if autosuspend >> is enabled. Is this acceptable? In my case I did enable autosuspend, but >> I have some doubts about this. > > I don't like to implement power management unless I have an application > that actually requires it. Otherwise, I consider it premature optimizatio= n. > It is difficult to know if we would be implementing it in a way that is > actually useful for a real-world use case. These chips seem like they > would mostly be used in an industrial setting, not in battery powered > applications, so I'm not sure anyone is going to worry about saving a few > milliamps. Makes sense. I can probably drop the autosuspend in that case. > >>=20 >>> >>> I have also pushed a branch to [3] that contains the start of some >>> documentation for this driver that can give some more insight into how >>> the implementation works. It still needs some work and also documents >>> some things that haven't been implemented yet, so I haven't included it >>> in this series yet. >>> >>> [3]: https://github.com/dlech/linux/blob/b4/iio-adc-ti-ads122c14/Docume= ntation/iio/ads112c14.rst >>> >>> Signed-off-by: David Lechner >>> --- >>> David Lechner (TI) (4): >>> dt-bindings: iio: adc: add ti,ads122c14 >>> iio: adc: add ti-ads112c14 driver >>> iio: adc: ti-ads112c14: implement gain on internal short SYS_MON = channel >>> iio: adc: ti-ads112c14: add measurement channel support >>> >>> .../devicetree/bindings/iio/adc/ti,ads112c14.yaml | 224 +++++ >>> MAINTAINERS | 8 + >>> drivers/iio/adc/Kconfig | 12 + >>> drivers/iio/adc/Makefile | 1 + >>> drivers/iio/adc/ti-ads112c14.c | 1053 ++++++++++++= ++++++++ >>> include/dt-bindings/iio/adc/ti,ads112c14.h | 11 + >>> 6 files changed, 1309 insertions(+) >>> --- >>> base-commit: ec039126b7fac4e3af35ebccaa7c6f9b6875ba81 >>> change-id: 20260514-iio-adc-ti-ads122c14-d0b92479334e >>> >>> Best regards, >>> -- =20 >>> David Lechner (TI) >>=20 --=20 Thanks, ~ Kurt