linux-kernel - RE: [PATCH v3 3/3] Documentation: ABI: adl8113: add documentation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID:
 <CY4PR03MB3399D2BCCF18EA13DCA768D49BD7A@CY4PR03MB3399.namprd03.prod.outlook.com>
Date: Wed, 19 Nov 2025 09:09:23 +0000
From: "Miclaus, Antoniu" <Antoniu.Miclaus@...log.com>
To: Jonathan Cameron <jic23@...nel.org>
CC: "robh@...nel.org" <robh@...nel.org>,
        "conor+dt@...nel.org"
	<conor+dt@...nel.org>,
        "linux-iio@...r.kernel.org"
	<linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>,
        David Lechner <dlechner@...libre.com>,
        "Sa,
 Nuno" <Nuno.Sa@...log.com>, Andy Shevchenko <andy@...nel.org>
Subject: RE: [PATCH v3 3/3] Documentation: ABI: adl8113: add documentation

 
> On Fri, 14 Nov 2025 11:57:25 +0000
> Antoniu Miclaus <antoniu.miclaus@...log.com> wrote:
> 
> > Add ABI documentation for the ADL8113 Low Noise Amplifier,
> > covering the 4 pin-selectable operating modes.
> >
> > Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> +CC all the IIO subsystem reviewers as I'm not sure how to handle
> what this device does, and would like some more opinions.
> 
> Anyone who has expertise or design experience with this sort
> of amplifier with external bypass path: how are these actually used?
> 
> The development board seems to just be suited to measurement of
> device characteristics, not representative of a design using it.
> 
> > ---
> >
> > Changes in v3:
> > - Replace "mode" attribute documentation with "signal_path" attribute
> > - Update descriptions to reflect separation of gain control (hardwaregain)
> and path control (signal_path)
> > - Add explanation of automatic bypass mode switching when selecting
> external paths
> > - Update attribute names from mode/mode_available to
> signal_path/signal_path_available
> > - Clarify that external paths enable connection of external components for
> filtering or amplification
> > ---
> >  .../testing/sysfs-bus-iio-amplifiers-adl8113  | 30 +++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-amplifiers-
> adl8113
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-iio-amplifiers-adl8113
> 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@...r.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
> > +		  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
> > +		  (VA=0, VB=1). External components can be connected for
> filtering or
> > +		  additional amplification. Automatically switches to bypass
> mode (0dB).
> > +
> > +		* external_b - Signal routes from RFIN to OUT_B and from
> IN_B to RFOUT
> > +		  (VA=1, VB=0). External components can be connected for
> filtering or
> > +		  additional amplification. Automatically switches to bypass
> mode (0dB).
> 
> I'm still not sure how to handle these external paths.  The one thing they won't
> be
> is truly zero gain (because that would be pointless given the internal bypass
> path does that).
> 
> So how are these used in practice?
> 
> Do we need to figure out how to describe the real characteristics of those
> paths?
> 
> All I could find is a brief reference in
> https://www.analog.com/en/resources/app-notes/an-2622.html
> to high dynamic range receiver applications. So with that as only breadcrumb
> my
> guess would be that they almost always have additional applifiers on those
> paths
> and we should figure out how to describe the aggregate device.

I managed to reach the applications engineer responsible of this part and indeed
the purpose of the external routing is to connect other LNAs or filters with different
gains.

That being said, I think David's second suggestion might be a way to go:

" Have the devicetree specify the gain of the two external bypass amplifiers
   so that we can use the hardwaregain attribute to select between the 4 mux
   positions without needing a custom attribute. This works as long as none
   of the amplifiers have the same gain."

Looking forward to your feedback so I can start implementing it in v4.

Thanks
> 
> A stop gap might be to merge the driver without this support till we figure out
> how to do it.
> 
> Jonathan
> 
> 
> > +
> > +		Note: Selecting an external path automatically sets the
> hardware gain
> > +		to 0dB (bypass mode) since external paths require bypass
> operation.
> > +
> > +What:
> 	/sys/bus/iio/devices/iio:deviceX/signal_path_available
> > +Date:		January 2025
> > +KernelVersion:	6.14
> > +Contact:	linux-iio@...r.kernel.org
> > +Description:
> > +		Reading this attribute returns a space-separated list of all
> > +		available signal paths for the ADL8113 device. The available
> paths
> > +		may depend on the current gain mode (hardwaregain setting).