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Message-ID: <5f0776ba5163578453e26352763ff1b4687bcf87.camel@gmail.com>
Subject: Re: [PATCH 1/3] dt-bindings: iio: adc: add AD4695 and similar ADCs
From: Nuno =?ISO-8859-1?Q?S=E1?= <noname.nuno@gmail.com>
To: David Lechner <dlechner@baylibre.com>, Krzysztof Kozlowski
 <krzk@kernel.org>,  Jonathan Cameron <jic23@kernel.org>, Rob Herring
 <robh@kernel.org>, Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley
 <conor+dt@kernel.org>
Cc: Michael Hennerich <michael.hennerich@analog.com>, Nuno
 =?ISO-8859-1?Q?S=E1?=
	 <nuno.sa@analog.com>, Jonathan Corbet <corbet@lwn.net>, 
	linux-iio@vger.kernel.org, devicetree@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org
Date: Thu, 13 Jun 2024 17:11:48 +0200
In-Reply-To: <b6b52b1e-847b-44ca-87f9-095a78164771@baylibre.com>
References: <20240612-iio-adc-ad4695-v1-0-6a4ed251fc86@baylibre.com>
	 <20240612-iio-adc-ad4695-v1-1-6a4ed251fc86@baylibre.com>
	 <94448c2c-e7b2-4191-858c-529b254994f1@kernel.org>
	 <f765ef30-a777-4dfc-8f93-0f15b46f91ae@baylibre.com>
	 <e09fecf4-bde2-4feb-8312-22c530c6a960@kernel.org>
	 <b6b52b1e-847b-44ca-87f9-095a78164771@baylibre.com>
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On Thu, 2024-06-13 at 09:39 -0500, David Lechner wrote:
> On 6/13/24 9:18 AM, Krzysztof Kozlowski wrote:
> > On 13/06/2024 15:57, David Lechner wrote:
> > >=20
> > > >=20
> > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - const: =
adi,ad4695
> > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - items:
> > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - const: =
adi,ad4697-wlcsp
> > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 - const: =
adi,ad4697
> > > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 # same chips with higher max samp=
le rate
> > >=20
> > > I suppose one could make the argument that the programming model is
> > > the same on these too, but the maximum sampling frequency does seem
> > > like an important bit of information so that you don't try to set
> > > the conversion trigger rate too high.
> > >=20
> >=20
> > which property is that? I don't see differences in the driver, so I
> > don't get how these wlcsp compatibles allow you to control value of
> > conversion trigger.
>=20
> This comment is unrelated to the package type (WLCSP or LFCSP).
>=20
> What I mean is that e.g. AD4695 and AD4696 are virtually identical
> other than the maximum allowable sample rate (500 kSPS or 1 MSPS).
>=20
> So my thinking was that it would make sense to have:
>=20
> 	compatible =3D "ad4695";
>=20
> for the lower sample rate chip and
>=20
> 	compatible =3D "ad4696", "ad4695";
>=20
> for the higher sample rate chip since ad4696 can do everything
> that ad4695 does plus a bit more.
>=20

IMO, that would make sense yes. If the higher sample rate chip fallsback, i=
t will
still work but not at full speed. The other way around is the one that we c=
an't allow
naturally.

But possibly dumb question now... since both devices will be supported at t=
he same
time, do we actually care about having the fallback compatible? My understa=
nding of
the fallback story is that we may load a DTS in an older kernel where chip =
A is
supported but chip B is not and it is ok for chip B to fallback to chip A. =
Since
these devices will be supported at the same time, do we need to care? Unles=
s out of
tree stuff enters the equation?

Or is there another usecase that I'm not aware about (or maybe it just make=
s sense to
document properly...)?

- Nuno S=C3=A1
>=20