Add below rounding related macros:

round_closest_up(x, y) : Rounds x to closest multiple of y where y is a
power of 2, with a preference to round up in case two nearest values are
possible.

round_closest_down(x, y) : Rounds x to closest multiple of y where y is a
power of 2, with a preference to round down in case two nearest values are
possible.

roundclosest(x, y) : Rounds x to closest multiple of y, this macro should
generally be used only when y is not multiple of 2 as otherwise
round_closest* macros should be used which are much faster.

Examples:
 * round_closest_up(17, 4) = 16
 * round_closest_up(15, 4) = 16
 * round_closest_up(14, 4) = 16
 * round_closest_down(17, 4) = 16
 * round_closest_down(15, 4) = 16
 * round_closest_down(14, 4) = 12
 * roundclosest(21, 5) = 20
 * roundclosest(19, 5) = 20
 * roundclosest(17, 5) = 15

Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
---
NOTE: This patch is inspired from the Mentor Graphics IPU driver [1]
which uses similar macro locally and which is updated in further patch
in the series 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

V9:
- No change

V8:
- Add new macro to round to nearest value for non-multiple of 2
- Update commit message as suggested:

V1->V6 (No change, patch introduced in V7)
---
 include/linux/math.h | 65 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/include/linux/math.h b/include/linux/math.h
index dd4152711de7..e2cc3769ed0e 100644
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -34,6 +34,54 @@
  */
 #define round_down(x, y) ((x) & ~__round_mask(x, y))
 
+/**
+ * round_closest_up - round closest to be multiple of specified value (which is
+ *                    power of 2) with preference to rounding up
+
+ * @x: the value to round
+ * @y: multiple to round closest to (must be a power of 2)
+ *
+ * Rounds @x to closest multiple of @y (which must be a power of 2).
+ * The value can be either rounded up or rounded down depending upon rounded
+ * value's closeness to the specified value. If there are two closest possible
+ * values, i.e. the difference between the specified value and it's rounded up
+ * and rounded down values is same then preference is given to rounded up
+ * value.
+ *
+ * To perform arbitrary rounding to closest value (not multiple of 2), use
+ * roundclosest().
+ *
+ * Examples :
+ * round_closest_up(17, 4) = 16
+ * round_closest_up(15, 4) = 16
+ * round_closest_up(14, 4) = 16
+ */
+#define round_closest_up(x, y) round_down((x) + (y) / 2, (y))
+
+/**
+ * round_closest_down - round closest to be multiple of specified value (which
+ *			is power of 2) with preference to rounding down
+ *
+ * @x: the value to round
+ * @y: multiple to round closest to (must be a power of 2)
+ *
+ * Rounds @x to closest multiple of @y (which must be a power of 2).
+ * The value can be either rounded up or rounded down depending upon rounded
+ * value's closeness to the specified value. If there are two closest possible
+ * values, i.e. the difference between the specified value and it's rounded up
+ * and rounded down values is same then preference is given to rounded up
+ * value.
+ *
+ * To perform arbitrary rounding to closest value (not multiple of 2), use
+ * roundclosest().
+ *
+ * Examples :
+ * round_closest_down(17, 4) = 16
+ * round_closest_down(15, 4) = 16
+ * round_closest_down(14, 4) = 12
+ */
+#define round_closest_down(x, y) round_up((x) - (y) / 2, (y))
+
 #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP
 
 #define DIV_ROUND_DOWN_ULL(ll, d) \
@@ -77,6 +125,23 @@
 }							\
 )
 
+/**
+ * roundclosest - round to nearest multiple
+ * @x: the value to round
+ * @y: multiple to round nearest to
+ *
+ * Rounds @x to nearest multiple of @y.
+ * The rounded value can be greater than or less than @x depending
+ * upon it's nearness to @x. If @y will always be a power of 2, consider
+ * using the faster round_closest_up() or round_closest_down().
+ *
+ * Examples :
+ * roundclosest(21, 5) = 20
+ * roundclosest(19, 5) = 20
+ * roundclosest(17, 5) = 15
+ */
+#define roundclosest(x, y) rounddown((x) + (y) / 2, (y))
+
 /*
  * Divide positive or negative dividend by positive or negative divisor
  * and round to closest integer. Result is undefined for negative
-- 
2.39.1

On Sun, May 26, 2024 at 11:38:56PM +0530, Devarsh Thakkar wrote:
> Add below rounding related macros:
> 
> round_closest_up(x, y) : Rounds x to closest multiple of y where y is a
> power of 2, with a preference to round up in case two nearest values are
> possible.
> 
> round_closest_down(x, y) : Rounds x to closest multiple of y where y is a
> power of 2, with a preference to round down in case two nearest values are
> possible.
> 
> roundclosest(x, y) : Rounds x to closest multiple of y, this macro should
> generally be used only when y is not multiple of 2 as otherwise
> round_closest* macros should be used which are much faster.
> 
> Examples:
>  * round_closest_up(17, 4) = 16
>  * round_closest_up(15, 4) = 16
>  * round_closest_up(14, 4) = 16
>  * round_closest_down(17, 4) = 16
>  * round_closest_down(15, 4) = 16
>  * round_closest_down(14, 4) = 12
>  * roundclosest(21, 5) = 20
>  * roundclosest(19, 5) = 20
>  * roundclosest(17, 5) = 15

...

> +/**
> + * round_closest_up - round closest to be multiple of specified value (which is
> + *                    power of 2) with preference to rounding up
> +

Not that big deal, but missing '*' here. Personally I would not even put
a blank line between Summary and Field Descriptions.

> + * @x: the value to round
> + * @y: multiple to round closest to (must be a power of 2)
> + *
> + * Rounds @x to closest multiple of @y (which must be a power of 2).
> + * The value can be either rounded up or rounded down depending upon rounded
> + * value's closeness to the specified value. If there are two closest possible
> + * values, i.e. the difference between the specified value and it's rounded up
> + * and rounded down values is same then preference is given to rounded up
> + * value.
> + *
> + * To perform arbitrary rounding to closest value (not multiple of 2), use
> + * roundclosest().
> + *
> + * Examples :

What is this suppose to be rendered to?

> + * round_closest_up(17, 4) = 16
> + * round_closest_up(15, 4) = 16
> + * round_closest_up(14, 4) = 16

Btw, is kernel-doc validator happy about all kernel docs you added?

> + */

-- 
With Best Regards,
Andy Shevchenko

Hi Andy,

Thanks for the review.

On 28/05/24 02:02, Andy Shevchenko wrote:
> On Sun, May 26, 2024 at 11:38:56PM +0530, Devarsh Thakkar wrote:
...

>> +/**
>> + * round_closest_up - round closest to be multiple of specified value (which is
>> + *                    power of 2) with preference to rounding up
>> +
> 
> Not that big deal, but missing '*' here. Personally I would not even put
> a blank line between Summary and Field Descriptions.
> 

My bad. Yes I would remove the blank line here. This is picked up as warning
from kernel-doc too.

>> + * @x: the value to round
>> + * @y: multiple to round closest to (must be a power of 2)
>> + *
>> + * Rounds @x to closest multiple of @y (which must be a power of 2).
>> + * The value can be either rounded up or rounded down depending upon rounded
>> + * value's closeness to the specified value. If there are two closest possible
>> + * values, i.e. the difference between the specified value and it's rounded up
>> + * and rounded down values is same then preference is given to rounded up
>> + * value.
>> + *
>> + * To perform arbitrary rounding to closest value (not multiple of 2), use
>> + * roundclosest().
>> + *
>> + * Examples :
> 
> What is this suppose to be rendered to?
> 

The file math.h is not rendered as part of kernel-doc right now. I can put
this under Documentation/core-api/kernel-api.rst perhaps I can create a new
section as below:

Rounding, absolute diff and 32bit division macros
-------------------------------------------------

under the section:
CRC and Math Functions in Linux

===============================

is that okay ?

>> + * round_closest_up(17, 4) = 16
>> + * round_closest_up(15, 4) = 16
>> + * round_closest_up(14, 4) = 16
> 
> Btw, is kernel-doc validator happy about all kernel docs you added?
> 

Yes, except the aforementioned blank line.

Regards
Devarsh

On Tue, May 28, 2024 at 04:02:30PM +0530, Devarsh Thakkar wrote:
> On 28/05/24 02:02, Andy Shevchenko wrote:
> > On Sun, May 26, 2024 at 11:38:56PM +0530, Devarsh Thakkar wrote:

...

> >> +/**
> >> + * round_closest_up - round closest to be multiple of specified value (which is
> >> + *                    power of 2) with preference to rounding up
> >> +
> > 
> > Not that big deal, but missing '*' here. Personally I would not even put
> > a blank line between Summary and Field Descriptions.
> 
> My bad. Yes I would remove the blank line here. This is picked up as warning
> from kernel-doc too.
> 
> >> + * @x: the value to round
> >> + * @y: multiple to round closest to (must be a power of 2)
> >> + *
> >> + * Rounds @x to closest multiple of @y (which must be a power of 2).
> >> + * The value can be either rounded up or rounded down depending upon rounded
> >> + * value's closeness to the specified value. If there are two closest possible
> >> + * values, i.e. the difference between the specified value and it's rounded up
> >> + * and rounded down values is same then preference is given to rounded up
> >> + * value.
> >> + *
> >> + * To perform arbitrary rounding to closest value (not multiple of 2), use
> >> + * roundclosest().
> >> + *
> >> + * Examples :
> > 
> > What is this suppose to be rendered to?
> 
> The file math.h is not rendered as part of kernel-doc right now. I can put
> this under Documentation/core-api/kernel-api.rst perhaps I can create a new
> section as below:
> 
> Rounding, absolute diff and 32bit division macros
> -------------------------------------------------
> 
> under the section:
> CRC and Math Functions in Linux
> 
> ===============================
> 
> is that okay ?

This is up to you, but what I meant is that you always can render manually
yourself. And I was asking about the result you got when you tried (and you
did, right?) to render to man, html, and pdf.

> >> + * round_closest_up(17, 4) = 16
> >> + * round_closest_up(15, 4) = 16
> >> + * round_closest_up(14, 4) = 16
> > 
> > Btw, is kernel-doc validator happy about all kernel docs you added?
> 
> Yes, except the aforementioned blank line.

-- 
With Best Regards,
Andy Shevchenko