media: v4l2-dv-timings: Introduce v4l2_calc_timeperframe helper

A new helper function was introduced to facilitate the calculation
of time per frame value whenever we have access to the full
v4l2_dv_timings structure.

This should be used only for receivers and only when there is
enough accuracy in the measured pixel clock value as well as in
the horizontal/vertical values.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/v4l2-core/v4l2-dv-timings.c

@@ -373,6 +373,45 @@ struct v4l2_fract v4l2_dv_timings_aspect_ratio(const struct v4l2_dv_timings *t)
 }
 EXPORT_SYMBOL_GPL(v4l2_dv_timings_aspect_ratio);
 
+/** v4l2_calc_timeperframe - helper function to calculate timeperframe based
+ *	v4l2_dv_timings fields.
+ * @t - Timings for the video mode.
+ *
+ * Calculates the expected timeperframe using the pixel clock value and
+ * horizontal/vertical measures. This means that v4l2_dv_timings structure
+ * must be correctly and fully filled.
+ */
+struct v4l2_fract v4l2_calc_timeperframe(const struct v4l2_dv_timings *t)
+{
+	const struct v4l2_bt_timings *bt = &t->bt;
+	struct v4l2_fract fps_fract = { 1, 1 };
+	unsigned long n, d;
+	u32 htot, vtot, fps;
+	u64 pclk;
+
+	if (t->type != V4L2_DV_BT_656_1120)
+		return fps_fract;
+
+	htot = V4L2_DV_BT_FRAME_WIDTH(bt);
+	vtot = V4L2_DV_BT_FRAME_HEIGHT(bt);
+	pclk = bt->pixelclock;
+
+	if ((bt->flags & V4L2_DV_FL_CAN_DETECT_REDUCED_FPS) &&
+	    (bt->flags & V4L2_DV_FL_REDUCED_FPS))
+		pclk = div_u64(pclk * 1000ULL, 1001);
+
+	fps = (htot * vtot) > 0 ? div_u64((100 * pclk), (htot * vtot)) : 0;
+	if (!fps)
+		return fps_fract;
+
+	rational_best_approximation(fps, 100, fps, 100, &n, &d);
+
+	fps_fract.numerator = d;
+	fps_fract.denominator = n;
+	return fps_fract;
+}
+EXPORT_SYMBOL_GPL(v4l2_calc_timeperframe);
+
 /*
  * CVT defines
  * Based on Coordinated Video Timings Standard

include/media/v4l2-dv-timings.h

@@ -10,6 +10,17 @@
 
 #include <linux/videodev2.h>
 
+/**
+ * v4l2_calc_timeperframe - helper function to calculate timeperframe based
+ *	v4l2_dv_timings fields.
+ * @t: Timings for the video mode.
+ *
+ * Calculates the expected timeperframe using the pixel clock value and
+ * horizontal/vertical measures. This means that v4l2_dv_timings structure
+ * must be correctly and fully filled.
+ */
+struct v4l2_fract v4l2_calc_timeperframe(const struct v4l2_dv_timings *t);
+
 /*
  * v4l2_dv_timings_presets: list of all dv_timings presets.
  */