drm/i915: Move abs_diff() to math.h

abs_diff() belongs to math.h. Move it there. This will allow others to
use it.

[[e-mail]: add abs_diff() documentation]
Link: https://lkml.kernel.org/r/[e-mail]
[[e-mail]: fix comment, per Randy]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Jiri Slaby <[e-mail]> # tty/serial
Acked-by: Jani Nikula <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>
Reviewed-by: Andi Shyti <[e-mail]>
Reviewed-by: Philipp Zabel <[e-mail]> # gpu/ipu-v3
Cc: Alexey Dobriyan <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: Imre Deak <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Joonas Lahtinen <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Cc: Tvrtko Ursulin <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

drivers/gpu/drm/i915/display/intel_dpll_mgr.c

···
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <linux/math.h>
 #include <linux/string_helpers.h>
 
 #include "i915_reg.h"

drivers/gpu/drm/i915/display/intel_dpll_mgr.h

···
 
 #include "intel_wakeref.h"
 
-/*FIXME: Move this to a more appropriate place. */
-#define abs_diff(a, b) ({			\
-	typeof(a) __a = (a);			\
-	typeof(b) __b = (b);			\
-	(void) (&__a == &__b);			\
-	__a > __b ? (__a - __b) : (__b - __a); })
-
 enum tc_port;
 struct drm_i915_private;
 struct intel_atomic_state;

drivers/gpu/ipu-v3/ipu-image-convert.c

···
 
 #include <linux/interrupt.h>
 #include <linux/dma-mapping.h>
+#include <linux/math.h>
+
 #include <video/imx-ipu-image-convert.h>
+
 #include "ipu-prv.h"
 
 /*
···
 		unsigned int in_pos;
 		unsigned int in_pos_aligned;
 		unsigned int in_pos_rounded;
-		unsigned int abs_diff;
+		unsigned int diff;
 
 		/*
 		 * Tiles in the right row / bottom column may not be allowed to
···
 		    (in_edge - in_pos_rounded) % in_burst)
 			continue;
 
-		if (in_pos < in_pos_aligned)
-			abs_diff = in_pos_aligned - in_pos;
-		else
-			abs_diff = in_pos - in_pos_aligned;
-
-		if (abs_diff < min_diff) {
+		diff = abs_diff(in_pos, in_pos_aligned);
+		if (diff < min_diff) {
 			in_seam = in_pos_rounded;
 			out_seam = out_pos;
-			min_diff = abs_diff;
+			min_diff = diff;
 		}
 	}
 

drivers/tty/serial/omap-serial.c

···
 				unsigned int baud, unsigned int mode)
 {
 	unsigned int n = port->uartclk / (mode * baud);
-	int abs_diff;
 
 	if (n == 0)
 		n = 1;
 
-	abs_diff = baud - (port->uartclk / (mode * n));
-	if (abs_diff < 0)
-		abs_diff = -abs_diff;
-
-	return abs_diff;
+	return abs_diff(baud, port->uartclk / (mode * n));
 }
 
 /*

drivers/video/fbdev/core/svgalib.c

···
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/fb.h>
+#include <linux/math.h>
 #include <linux/svga.h>
 #include <asm/types.h>
 #include <asm/io.h>
···
  *  F_VCO = (F_BASE * M) / N
  *  F_OUT = F_VCO / (2^R)
  */
-
-static inline u32 abs_diff(u32 a, u32 b)
-{
-	return (a > b) ? (a - b) : (b - a);
-}
-
 int svga_compute_pll(const struct svga_pll *pll, u32 f_wanted, u16 *m, u16 *n, u16 *r, int node)
 {
 	u16 am, an, ar;

include/linux/math.h

···
 	({ signed type __x = (x); __x < 0 ? -__x : __x; }), other)
 
 /**
+ * abs_diff - return absolute value of the difference between the arguments
+ * @a: the first argument
+ * @b: the second argument
+ *
+ * @a and @b have to be of the same type. With this restriction we compare
+ * signed to signed and unsigned to unsigned. The result is the subtraction
+ * the smaller of the two from the bigger, hence result is always a positive
+ * value.
+ *
+ * Return: an absolute value of the difference between the @a and @b.
+ */
+#define abs_diff(a, b) ({			\
+	typeof(a) __a = (a);			\
+	typeof(b) __b = (b);			\
+	(void)(&__a == &__b);			\
+	__a > __b ? (__a - __b) : (__b - __a);	\
+})
+
+/**
  * reciprocal_scale - "scale" a value into range [0, ep_ro)
  * @val: value
  * @ep_ro: right open interval endpoint