linux-kernel - Re: [PATCH] w1: therm: Use clamp_t to simplify int_to

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Message-Id: <28C4DAF0-91B9-4175-AC2C-D3B5AC283439@linux.dev>
Date: Sun, 9 Nov 2025 21:30:00 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: David Laight <david.laight.linux@...il.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
 Huisong Li <lihuisong@...wei.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] w1: therm: Use clamp_t to simplify int_to_short helper

On 9. Nov 2025, at 17:20, David Laight wrote:
> On Sun,  9 Nov 2025 13:59:55 +0100
> Thorsten Blum <thorsten.blum@...ux.dev> wrote:
> 
>> Use clamp_t() instead of manually casting the return value.
>> 
>> Replace sprintf() with sysfs_emit() to improve sysfs show functions
>> while we're at it.
>> 
>> ...
>> +	/* Cast to short by eliminating out of range values */
>                  ^^^^^ no shorts here...

It's even shorter than short. I didn't even notice...

>> +	return clamp_t(s8, i, MIN_TEMP, MAX_TEMP);
> 
> That is just plain broken.
> clamp_t() really shouldn't have been allowed to exist.
> That is a typical example of how it gets misused.
> (min_t() and max_t() get misused the same way.)
> 
> Think what happens when i is 256.
> The code should just be:
> 
> 	return clamp(i, MIN_TEMP, MAX_TEMP);
> 
> No casts anywhere.

Ok, yeah 256 would be 0 when cast to s8 even though it should be clamped
to MAX_TEMP. Never thought about this side effect of clamp_t(). Will
change it to just clamp() in v2, thanks!

> I'm not even sure the return type (s8) makes any sense.
> It is quite likely that the code will be better if it is 'int'.
> The fact that the domain in inside -128..127 doesn't mean that
> the correct type for a variable isn't 'int'.

The low and high temperatures (s8) are only written to the u8 array
'new_config_register' for which s8 seems fine. What made you think int
might be better?

Thanks,
Thorsten