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

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Date:   Fri, 20 Oct 2023 16:31:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Balas, Eliza" <Eliza.Balas@...log.com>
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

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?

> Since the device is not an iio device, using an iio function would be confusing.

Why isn't this an iio device?

thanks,

greg k-h