linux-kernel - Re: [PATCH v6 2/3] iio: light: add support for veml6046x00 RGBIR color sensor

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Message-ID: <4d4120fa-3a20-4cc4-a078-ee94e03229f9@gmail.com>
Date: Fri, 22 Aug 2025 08:39:35 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Andreas Klinger <ak@...klinger.de>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: jic23@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, lars@...afoo.de, javier.carrasco.cruz@...il.com,
 arthur.becker@...tec.com, perdaniel.olsson@...s.com,
 mgonellabolduc@...onoff.com, muditsharma.info@...il.com, clamor95@...il.com,
 emil.gedenryd@...s.com, devicetree@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/3] iio: light: add support for veml6046x00 RGBIR
 color sensor

On 21/08/2025 21:53, Andreas Klinger wrote:
> Hi Andy,
> 
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> schrieb am Do, 21. Aug 12:43:
>>>>> +	part_id = le16_to_cpu(reg);
>>>>> +	if (part_id != 0x0001)
>>>>> +		dev_info(dev, "Unknown ID %#04x\n", part_id);
>>>>
>>>> For 0 it will print 0 and not 0x0000. Is it okay?
>>>
>>> I just tried and it prints 0x00 if the part_id is 0.
>>
>> This is interesting... So it's not 0, nor 0x0000?
> 
> No. It prints 0x00 on my BeagleBoneBlack with kernel 6.16.0-rc5.

I think this makes sense because of the '#' -flag. The "0x" is appended 
because of it, and this consumes 2 characters from the 4 character 
field, leaving only 2 chars left for the value.

What I find interesting is that gcc on my PC does:

         printf("%#04x\n", 0);
         printf("%#04x\n", 1);
         printf("%#04x\n", 10);
         printf("%#04x\n", 17);

0000
0x01
0x0a
0x11

gcc version 15.2.1 20250808 (Red Hat 15.2.1-1) (GCC)

It'd be nice to learn why the zero is treated differently? Andy, did you 
have some insight as you asked this?

Yours,
	-- Matti