linux-kernel - RE: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine

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Date:   Mon, 23 Oct 2023 12:54:15 +0000
From:   "Balas, Eliza" <Eliza.Balas@...log.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Derek Kiernan <derek.kiernan@....com>,
        Dragan Cvetic <dragan.cvetic@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: RE: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine

> -----Original Message-----
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Sent: Friday, October 20, 2023 17:32
> To: Balas, Eliza <Eliza.Balas@...log.com>
> Cc: linux-kernel@...r.kernel.org; devicetree@...r.kernel.org; Rob Herring <robh+dt@...nel.org>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@...aro.org>; Conor Dooley <conor+dt@...nel.org>; Derek Kiernan <derek.kiernan@....com>; Dragan
> Cvetic <dragan.cvetic@....com>; Arnd Bergmann <arnd@...db.de>
> Subject: Re: [PATCH v3 2/2] drivers: misc: adi-axi-tdd: Add TDD engine
> 
> [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 = READ_ONCE(st->clk.rate);
> > > > +	char *orig_str, *modf_str, *int_part, frac_part[7];
> > > > +	long ival, frac;
> > > > +	int ret;
> > > > +
> > > > +	orig_str = kstrdup(buf, GFP_KERNEL);
> > > > +	int_part = strsep(&orig_str, ".");
> > >
> > > Why are we parsing floating point in the kernel?  Please just keep 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 are
> 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 value.
> 
> 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 values,
than using a lot of zeros for nanoseconds. I will make the changes
to accept values in nanoseconds..

> > 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.