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From:   "Balas, Eliza" <Eliza.Balas@analog.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Derek Kiernan <derek.kiernan@amd.com>,
        Dragan Cvetic <dragan.cvetic@amd.com>,
        Arnd Bergmann <arnd@arndb.de>
Subject: RE: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine
Thread-Topic: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine
Thread-Index: AQHaAow+3kwQRklh0USw0Mt3uyHh0rBRZjoAgAEeXwCAADqhAIAEjRKQgAAQXYCAAANoYA==
Date:   Mon, 23 Oct 2023 13:30:21 +0000
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> -----Original Message-----
> From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Sent: Monday, October 23, 2023 16:00
> To: Balas, Eliza <Eliza.Balas@analog.com>
> Cc: linux-kernel@vger.kernel.org; devicetree@vger.kernel.org; Rob Herring=
 <robh+dt@kernel.org>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@linaro.org>; Conor Dooley <conor+dt@kernel.org>; =
Derek Kiernan <derek.kiernan@amd.com>; Dragan
> Cvetic <dragan.cvetic@amd.com>; Arnd Bergmann <arnd@arndb.de>
> Subject: Re: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine
>=20
> [External]
>=20
> On Mon, Oct 23, 2023 at 12:54:15PM +0000, Balas, Eliza wrote:
> > > -----Original Message-----
> > > From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Sent: Friday, October 20, 2023 17:32
> > > To: Balas, Eliza <Eliza.Balas@analog.com>
> > > Cc: linux-kernel@vger.kernel.org; devicetree@vger.kernel.org; Rob Her=
ring <robh+dt@kernel.org>; Krzysztof Kozlowski
> > > <krzysztof.kozlowski+dt@linaro.org>; Conor Dooley <conor+dt@kernel.or=
g>; Derek Kiernan <derek.kiernan@amd.com>; Dragan
> > > Cvetic <dragan.cvetic@amd.com>; Arnd Bergmann <arnd@arndb.de>
> > > Subject: Re: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engin=
e
> > >
> > > [External]
> > >
> > > On Fri, Oct 20, 2023 at 11:18:44AM +0000, Balas, Eliza wrote:
> > > > > > +static int adi_axi_tdd_parse_ms(struct adi_axi_tdd_state *st,
> > > > > > +				const char *buf,
> > > > > > +				u64 *res)
> > > > > > +{
> > > > > > +	u64 clk_rate =3D READ_ONCE(st->clk.rate);
> > > > > > +	char *orig_str, *modf_str, *int_part, frac_part[7];
> > > > > > +	long ival, frac;
> > > > > > +	int ret;
> > > > > > +
> > > > > > +	orig_str =3D kstrdup(buf, GFP_KERNEL);
> > > > > > +	int_part =3D strsep(&orig_str, ".");
> > > > >
> > > > > Why are we parsing floating point in the kernel?  Please just kee=
p the
> > > > > api simple so that we don't have to try to do any type of parsing=
 other
> > > > > than turning a single text number into a value.
> > > > >
> > > >
> > > > The adi_axi_tdd_parse_ms function does almost the same thing as the
> > > > iio_str_to_fixpoint() function which already exists in kernel.
> > >
> > > That does not mean that this is a valid api for your device as you ar=
e
> > > not an iio driver (why aren't you an iio driver?)
> > >
> > > > It parses a fixed-point number from a string.
> > >
> > > And as such, you shouldn't duplicate existing logic.
> > >
> > > > The __iio_str_to_fixpoint is used in a similar way, as I intend to =
use adi_axi_tdd_parse_ms.
> > > > It writes to a channel the corresponding scale (micro,nano) for a v=
alue.
> > >
> > > Why not just have the api accept values in nanoseconds and then no
> > > parsing is needed?
> >
> > I thought this would be easier for the user, to work with smaller value=
s,
> > than using a lot of zeros for nanoseconds. I will make the changes
> > to accept values in nanoseconds..
>=20
> Make the kernel simpler, it's easier to make more complex userspace,
> right?
>=20
> > > > Since the device is not an iio device, using an iio function would =
be confusing.
> > >
> > > Why isn't this an iio device?
> >
> > The device is not registered into the IIO device tree,
> > and does not rely on IIO kernel APIs.
> > Even though there are a few attributes that resemble the
> > ones from iio, and the sysfs structure is similar,
> > this is not an IIO device.
> > In the previous patch versions 1 and 2 we concluded
> > that this device fits better in the misc subsystem.
>=20
> Ok, can you point to that in the changelog where the IIO maintainer
> agreed that this doesn't fit into that subsystem?
>=20
This was one of the discussions from previous v2 : https://lore.kernel.org/=
all/5b6318f16799e6e2575fe541e83e42e0afebe6cf.camel@gmail.com/

I will add it to the changelog the next time I submit the patches.

Thank you,
Eliza