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

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Date: Fri, 10 May 2024 18:15:34 +0300
From: Jani Nikula <jani.nikula@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Devarsh Thakkar
 <devarsht@...com>
Cc: 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 Fri, 10 May 2024, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> On Fri, May 10, 2024 at 12:09:52AM +0530, Devarsh Thakkar wrote:
>> Add macros to round to nearest specified power of 2.
>
> This is not what they are doing. For the above we already have macros defined.
>
>> Two macros are added :
>
> (Yes, after I wrapped to comment this line looks better on its own,
>  so whatever will be the first sentence, this line should be separated
>  from.)
>
>> round_closest_up and round_closest_down which round up to nearest multiple
>
> round_closest_up() and round_closest_down()
>
>
>> of 2 with a preference to round up or round down respectively if there are
>> two possible nearest values to the given number.
>
> You should reformulate, because AFAICS there is the crucial difference
> from these and existing round_*_pow_of_two().

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()?

BR,
Jani.


>
>> This patch is inspired from the Mentor Graphics IPU driver [1] which uses
>> similar macro locally and which can be updated to use this generic macro
>> instead along with other drivers having similar requirements.
>> 
>> [1]:
>> https://elixir.bootlin.com/linux/v6.8.9/source/drivers/gpu/ipu-v3/ipu-image-convert.c#L480
>
> Instead of this, just add a patch to convert that driver to use this new macro.
> Besides, this paragraph should go to the comment/changelog area below.
>
>> Signed-off-by: Devarsh Thakkar <devarsht@...com>
>> ---
>> V1->V6 (No change, patch introduced in V7)
>> ---

-- 
Jani Nikula, Intel