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([2001:818:ea56:d000:94c4:fb0e:28f:2a8d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b5ce849ddsm24157607f8f.14.2025.11.18.00.07.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Nov 2025 00:07:41 -0800 (PST) Message-ID: <62109f602caefd06a23bbd96e05c327647d054e9.camel@gmail.com> Subject: Re: [PATCH v3 3/3] Documentation: ABI: adl8113: add documentation From: Nuno =?ISO-8859-1?Q?S=E1?= To: David Lechner , Jonathan Cameron , Antoniu Miclaus Cc: robh@kernel.org, conor+dt@kernel.org, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, Nuno =?ISO-8859-1?Q?S=E1?= , Andy Shevchenko Date: Tue, 18 Nov 2025 08:08:44 +0000 In-Reply-To: References: <20251114115725.5660-1-antoniu.miclaus@analog.com> <20251114115725.5660-4-antoniu.miclaus@analog.com> <20251116155013.2b55af25@jic23-huawei> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-11-17 at 17:59 -0600, David Lechner wrote: > On 11/16/25 9:50 AM, Jonathan Cameron wrote: > > On Fri, 14 Nov 2025 11:57:25 +0000 > > Antoniu Miclaus wrote: > >=20 > > > Add ABI documentation for the ADL8113 Low Noise Amplifier, > > > covering the 4 pin-selectable operating modes. > > >=20 > > > Signed-off-by: Antoniu Miclaus > > +CC all the IIO subsystem reviewers as I'm not sure how to handle > > what this device does, and would like some more opinions. > >=20 > > Anyone who has expertise or design experience with this sort > > of amplifier with external bypass path: how are these actually used? > >=20 > > The development board seems to just be suited to measurement of > > device characteristics, not representative of a design using it. > >=20 > > > --- > > >=20 > > > Changes in v3: > > > - Replace "mode" attribute documentation with "signal_path" attribute > > > - Update descriptions to reflect separation of gain control (hardware= gain) and > > > path control (signal_path) > > > - Add explanation of automatic bypass mode switching when selecting e= xternal > > > paths > > > - Update attribute names from mode/mode_available to > > > signal_path/signal_path_available > > > - Clarify that external paths enable connection of external component= s for > > > filtering or amplification > > > --- > > > =C2=A0.../testing/sysfs-bus-iio-amplifiers-adl8113=C2=A0 | 30 +++++++= ++++++++++++ > > > =C2=A01 file changed, 30 insertions(+) > > > =C2=A0create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-ampl= ifiers-adl8113 > > >=20 > > > diff --git a/Documentation/ABI/testing/sysfs-bus-iio-amplifiers-adl81= 13 > > > b/Documentation/ABI/testing/sysfs-bus-iio-amplifiers-adl8113 > > > new file mode 100644 > > > index 000000000000..31fb1e6e80fc > > > --- /dev/null > > > +++ b/Documentation/ABI/testing/sysfs-bus-iio-amplifiers-adl8113 > > > @@ -0,0 +1,30 @@ > > > +What: /sys/bus/iio/devices/iio:deviceX/signal_path > > > +Date: January 2025 > > > +KernelVersion: 6.14 > > > +Contact: linux-iio@vger.kernel.org > > > +Description: > > > + This attribute controls the signal routing path for the > > > ADL8113 > > > + Low Noise Amplifier. The supported signal paths are: > > > + > > > + * internal - Signal passes through internal path. Can be used > > > with > > > + =C2=A0 either amplifier mode (14dB gain) or bypass mode (0dB gain)= . > > > + > > > + * external_a - Signal routes from RFIN to OUT_A and from IN_A > > > to RFOUT > > > + =C2=A0 (VA=3D0, VB=3D1). External components can be connected for > > > filtering or > > > + =C2=A0 additional amplification. Automatically switches to bypass > > > mode (0dB). > > > + > > > + * external_b - Signal routes from RFIN to OUT_B and from IN_B > > > to RFOUT > > > + =C2=A0 (VA=3D1, VB=3D0). External components can be connected for > > > filtering or > > > + =C2=A0 additional amplification. Automatically switches to bypass > > > mode (0dB). > >=20 > > I'm still not sure how to handle these external paths.=C2=A0 The one th= ing they won't > > be > > is truly zero gain (because that would be pointless given the internal = bypass > > path does that). > >=20 > > So how are these used in practice? >=20 > Afraid I don't have any experience with this. But I would assume that the= two > external > bypasses each have another amplifier (or attenuator) connected to them. >=20 Unfortunately me neither. Antoniu, it would make sense to figure out who th= e APPs engineer for this part is. He is the one who can answer how the bypass feat= ure is supposed to be used in practise. > >=20 > > Do we need to figure out how to describe the real characteristics of th= ose paths? >=20 > It sounds like this is just a multiplexer. So a few ideas: >=20 > 1. We could handle this like iio-mux.c and have 4 channels and just restr= ict use > =C2=A0=C2=A0 to one channel at a time. Not exactly sure how we would do t= hat. Perhaps an > =C2=A0=C2=A0 enable attribute that is interlocked so that it will fail to= enable if another > =C2=A0=C2=A0 channel is already enabled? In this case, the devicetree wou= ld need to have an > =C2=A0=C2=A0 io-channels property to get the two bypass amplifier channel= s and basically pass > =C2=A0=C2=A0 them through. >=20 > 2. Have the devicetree specify the gain of the two external bypass amplif= iers > =C2=A0=C2=A0 so that we can use the hardwaregain attribute to select betw= een the 4 mux > =C2=A0=C2=A0 positions without needing a custom attribute. This works as = long as none > =C2=A0=C2=A0 of the amplifiers have the same gain. >=20 > I'm envisioning this would be e.g. part of a range selection on some sort= of > test equipment. In that case, option 2 seems the right way to go about it= . This makes sense but I would still try to have some confirmation about this= . - Nuno S=C3=A1 >=20