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

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Date: Fri, 10 May 2024 14:06:55 +0530
From: Devarsh Thakkar <devarsht@...com>
To: <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>,
        <andriy.shevchenko@...ux.intel.com>, <adobriyan@...il.com>,
        <jani.nikula@...el.com>, <p.zabel@...gutronix.de>, <airlied@...il.com>,
        <daniel@...ll.ch>, <dri-devel@...ts.freedesktop.org>
CC: <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>, <devarsht@...com>, <andrzej.p@...labora.com>,
        <nicolas@...fresne.ca>
Subject: [PATCH RESEND v7 6/8] math.h Add macros to round to closest specified power of 2

Add macros to round to nearest specified power of 2. Two macros are added :
round_closest_up and round_closest_down which round up to nearest multiple
of 2 with a preference to round up or round down respectively if there are
two possible nearest values to the given number.

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

Signed-off-by: Devarsh Thakkar <devarsht@...com>
---
V1->V6 (No change, patch introduced in V7)
---
 include/linux/math.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/include/linux/math.h b/include/linux/math.h
index dd4152711de7..82ee3265c910 100644
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -34,6 +34,42 @@
  */
 #define round_down(x, y) ((x) & ~__round_mask(x, y))
 
+/**
+ * round_closest_up - round to nearest specified power of 2 with preference
+ *		      to rounding up
+ * @x: the value to round
+ * @y: multiple to round to (must be a power of 2)
+ *
+ * Rounds @x to nearest multiple of @y (which must be a power of 2).
+ * The rounded value can be greater than or less than @x depending
+ * upon it's nearness to @x. If there are two nearest possible values,
+ * then preference will be given to the greater value.
+ *
+ * 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 to nearest specified power of 2 with preference
+ *			to rounding down
+ * @x: the value to round
+ * @y: multiple to round down to (must be a power of 2)
+ *
+ * Rounds @x to nearest multiple of @y (which must be a power of 2).
+ * The rounded value can be greater than or less than @x depending
+ * upon it's nearness to @x. If there are two nearest possible values,
+ * then preference will be given to the lesser value.
+ *
+ * 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) \
-- 
2.39.1