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

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Date:   Fri, 20 Oct 2023 13:26:05 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Balas, Eliza" <Eliza.Balas@...log.com>,
        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

On 20/10/2023 13:18, Balas, Eliza wrote:
>> -----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.

Why did you skip other comments?

Best regards,
Krzysztof