linux-kernel - Re: [PATCH v7 6/8] math.h Add macros to round to closest specified power of 2

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Date: Mon, 13 May 2024 11:59:25 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Devarsh Thakkar <devarsht@...com>
Cc: Jani Nikula <jani.nikula@...el.com>, mchehab@...nel.org,
	hverkuil-cisco@...all.nl, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, benjamin.gaignard@...labora.com,
	sebastian.fricke@...labora.com, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, adobriyan@...il.com,
	p.zabel@...gutronix.de, airlied@...il.com, daniel@...ll.ch,
	dri-devel@...ts.freedesktop.org, laurent.pinchart@...asonboard.com,
	praneeth@...com, nm@...com, vigneshr@...com, a-bhatia1@...com,
	j-luthra@...com, b-brnich@...com, detheridge@...com,
	p-mantena@...com, vijayp@...com, andrzej.p@...labora.com,
	nicolas@...fresne.ca
Subject: Re: [PATCH v7 6/8] math.h Add macros to round to closest specified
 power of 2

On Sat, May 11, 2024 at 11:11:14PM +0530, Devarsh Thakkar wrote:
> On 10/05/24 20:45, Jani Nikula wrote:

[...]

> > Moreover, I think the naming of round_up() and round_down() should have
> > reflected the fact that they operate on powers of 2. It's unfortunate
> > that the difference to roundup() and rounddown() is just the underscore!
> > That's just a trap.
> > 
> > So let's perhaps not repeat the same with round_closest_up() and
> > round_closest_down()?
> 
> Yes the naming is inspired by existing macros i.e. round_up, round_down
> (which round up/down to next pow of 2) and DIV_ROUND_CLOSEST (which
> round the divided value to closest value) and there are already a lot of
> users for these API's :
> 
>   linux-next git:(heads/next-20240509) ✗ grep -nr round_up drivers | wc
>     730    4261   74775
> 
>   linux-next git:(heads/next-20240509) ✗ grep -nr round_down drivers | wc
>     226    1293   22194
> 
>  linux-next git:(heads/next-20240509) ✗ grep -nr DIV_ROUND_CLOSEST
> drivers | wc
>    1207    7461  111822

Side note, discover `git grep ...`: it's much much faster on Git index,
than classic one on a working copy.

> so I thought to align with existing naming convention assuming
> developers are already familiar with this.
> 
> But if a wider consensus is to go with a newer naming convention then I
> am open to it, although a challenge there would be to keep it short. For
> e.g. this one is already 3 words, if we go with more explicit
> "round_closest_up_pow_2" it looks quite long in my opinion :) .

You need properly name the macros. Again, round_up() / roundup() and
roundup_pow_of_two() are three _different_ macros, and it's not clear
why you can't use one of them in your case.

The patch that changes those to a new one are doubtful to begin with.
I.e. need a careful review on the arithmetics side of the change
including HW capabilities of handling "closest" results.

-- 
With Best Regards,
Andy Shevchenko