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

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Date:   Fri, 20 Oct 2023 11:18:44 +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: Thursday, October 19, 2023 20:57
> 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 Thu, Oct 19, 2023 at 03:56:46PM +0300, Eliza Balas wrote:
> > +config ADI_AXI_TDD
> > +	tristate "Analog Devices TDD Engine support"
> > +	depends on HAS_IOMEM
> > +	select REGMAP_MMIO
> > +	help
> > +	  The ADI AXI TDD core is the reworked and generic TDD engine which
> > +	  was developed for general use in Analog Devices HDL projects. Unlike
> > +	  the previous TDD engine, this core can only be used standalone mode,
> > +	  and is not embedded into other devices.
> 
> What does "previous" mean here?  That's not relevant for a kernel help
> text, is it?
> 
> Also, what is the module name?  Why would someone enable this?  What
> userspace tools use it?
> 
> 
> > +
> >  config DUMMY_IRQ
> >  	tristate "Dummy IRQ handler"
> >  	help
> 
> Why put your entry in this specific location in the file?
> 
> > +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.
It parses a fixed-point number from a string. 
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.

Since the device is not an iio device, using an iio function would be confusing.
That is the reason for creating the adi_axi_tdd_parse_ms function, which is easier
to understand since I don't have to make all the multiplications that are made 
in the __iio_str_to_fixpoint function.

Thank you for review,
Eliza