V4L/DVB (11901): v4l2: Create helper function for bounding and aligning images

Most hardware has limits on minimum and maximum image dimensions and also
requirements about alignment.  For example, image width must be even or a
multiple of four.  Some hardware has requirements that the total image size
(width * height) be a multiple of some power of two.

v4l_bound_align_image() will enforce min and max width and height, power of
two alignment on width and height, and power of two alignment on total
image size.

It uses an efficient algorithm that will try to find the "closest" image
size that meets the requirements.
Signed-off-by: NTrent Piepho <xyzzy@speakeasy.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-common.c

@@ -1021,4 +1021,77 @@ const unsigned short *v4l2_i2c_tuner_addrs(enum v4l2_i2c_tuner_type type)
 }
 EXPORT_SYMBOL_GPL(v4l2_i2c_tuner_addrs);
 
-#endif
+/* Clamp x to be between min and max, aligned to a multiple of 2^align.  min
+ * and max don't have to be aligned, but there must be at least one valid
+ * value.  E.g., min=17,max=31,align=4 is not allowed as there are no multiples
+ * of 16 between 17 and 31.  */
+static unsigned int clamp_align(unsigned int x, unsigned int min,
+				unsigned int max, unsigned int align)
+{
+	/* Bits that must be zero to be aligned */
+	unsigned int mask = ~((1 << align) - 1);
+
+	/* Round to nearest aligned value */
+	if (align)
+		x = (x + (1 << (align - 1))) & mask;
+
+	/* Clamp to aligned value of min and max */
+	if (x < min)
+		x = (min + ~mask) & mask;
+	else if (x > max)
+		x = max & mask;
+
+	return x;
+}
+
+/* Bound an image to have a width between wmin and wmax, and height between
+ * hmin and hmax, inclusive.  Additionally, the width will be a multiple of
+ * 2^walign, the height will be a multiple of 2^halign, and the overall size
+ * (width*height) will be a multiple of 2^salign.  The image may be shrunk
+ * or enlarged to fit the alignment constraints.
+ *
+ * The width or height maximum must not be smaller than the corresponding
+ * minimum.  The alignments must not be so high there are no possible image
+ * sizes within the allowed bounds.  wmin and hmin must be at least 1
+ * (don't use 0).  If you don't care about a certain alignment, specify 0,
+ * as 2^0 is 1 and one byte alignment is equivalent to no alignment.  If
+ * you only want to adjust downward, specify a maximum that's the same as
+ * the initial value.
+ */
+void v4l_bound_align_image(u32 *w, unsigned int wmin, unsigned int wmax,
+			   unsigned int walign,
+			   u32 *h, unsigned int hmin, unsigned int hmax,
+			   unsigned int halign, unsigned int salign)
+{
+	*w = clamp_align(*w, wmin, wmax, walign);
+	*h = clamp_align(*h, hmin, hmax, halign);
+
+	/* Usually we don't need to align the size and are done now. */
+	if (!salign)
+		return;
+
+	/* How much alignment do we have? */
+	walign = __ffs(*w);
+	halign = __ffs(*h);
+	/* Enough to satisfy the image alignment? */
+	if (walign + halign < salign) {
+		/* Max walign where there is still a valid width */
+		unsigned int wmaxa = __fls(wmax ^ (wmin - 1));
+		/* Max halign where there is still a valid height */
+		unsigned int hmaxa = __fls(hmax ^ (hmin - 1));
+
+		/* up the smaller alignment until we have enough */
+		do {
+			if (halign >= hmaxa ||
+			    (walign <= halign && walign < wmaxa)) {
+				*w = clamp_align(*w, wmin, wmax, walign + 1);
+				walign = __ffs(*w);
+			} else {
+				*h = clamp_align(*h, hmin, hmax, halign + 1);
+				halign = __ffs(*h);
+			}
+		} while (halign + walign < salign);
+	}
+}
+EXPORT_SYMBOL_GPL(v4l_bound_align_image);
+#endif /* defined(CONFIG_I2C) */

include/media/v4l2-common.h

@@ -209,4 +209,14 @@ struct v4l2_routing {
 	u32 output;
 };
 
+/* ------------------------------------------------------------------------- */
+
+/* Miscellaneous helper functions */
+
+void v4l_bound_align_image(unsigned int *w, unsigned int wmin,
+			   unsigned int wmax, unsigned int walign,
+			   unsigned int *h, unsigned int hmin,
+			   unsigned int hmax, unsigned int halign,
+			   unsigned int salign);
+
 #endif /* V4L2_COMMON_H_ */