linux-kernel - Re: [PATCH 2/7] iio: inkern: Add API for reading/writing events

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Message-ID: <f180b5ac-131f-474a-be5e-70787972a772@linux.dev>
Date: Thu, 17 Jul 2025 12:42:13 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Jean Delvare <jdelvare@...e.com>,
 Guenter Roeck <linux@...ck-us.net>, linux-iio@...r.kernel.org,
 linux-hwmon@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
 Nuno Sá <nuno.sa@...log.com>, linux-kernel@...r.kernel.org,
 David Lechner <dlechner@...libre.com>
Subject: Re: [PATCH 2/7] iio: inkern: Add API for reading/writing events

On 7/16/25 05:28, Andy Shevchenko wrote:
> On Tue, Jul 15, 2025 at 11:42:05AM -0400, Sean Anderson wrote:
>> On 7/15/25 04:18, Andy Shevchenko wrote:
>> > On Mon, Jul 14, 2025 at 09:20:18PM -0400, Sean Anderson wrote:
> 
> ...
> 
>> >> +EXPORT_SYMBOL_GPL(iio_event_mode);
>> > 
>> > Can we move this to namespace? Otherwise it will be never ending story...
>> > Ditto for other new APIs.
>> 
>> Never ending story of what?
> 
> Of converting IIO core to use exported namespaces.

What's the purpose?

>> >> +			if (scale64 <= INT_MAX && scale64 >= INT_MIN)
>> >> +				raw64 = processed / (int)scale64;
>> > 
>> > Do you need the casting? (I mean if the compiler is dumb enough to not see this)
>> 
>> AIUI 64-bit division is not available on 32-bit platforms. The cast
>> ensures we get 32-bit division.
> 
> I put specifically a remark in the parentheses. So, the Q is if the compiler
> doesn't recognize that. Can you confirm that 32-bit compilation without cast
> is broken?

inkern.c:(.text.iio_write_event_processed_scale+0x14c): undefined reference to `__aeabi_ldivmod'

>> >> +	*raw = clamp(raw64, (s64)INT_MIN, (s64)INT_MAX);
>> > 
>> > You already have similar approach here...
>> 
>> Well, I can spell it 0x7fffffffLL if you'd like...
> 
> Nope, I like to have named constants instead of magics, but actually are those
> castings needed for the clamp()?

Apparently not. The checks in __clamp_once are only for matching signedness. And
the ints are promoted to s64s when the comparison is made.

--Sean