[media] omap3isp: resizer: Use 4-tap mode equations when the ratio is <= 512

As the number of phases/taps, used to select the correct equations to
compute the ratio, depends on the ratio, start with the 7-tap mode
equations to compute an approximation of the ratio, and switch to the
4-tap mode equations if the approximation is lower than or equal to 512.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/omap3isp/ispresizer.c

@@ -724,9 +724,20 @@ static void resizer_print_status(struct isp_res_device *res)
  *	vrsz = ((ih - 7) * 256 - 32 - 64 * spv) / (oh - 1)
  *
  * The ratios are integer values, and must be rounded down to ensure that the
- * cropped input size is not bigger than the uncropped input size. As the ratio
- * in 7-tap mode is always smaller than the ratio in 4-tap mode, we can use the
- * 7-tap mode equations to compute a ratio approximation.
+ * cropped input size is not bigger than the uncropped input size.
+ *
+ * As the number of phases/taps, used to select the correct equations to compute
+ * the ratio, depends on the ratio, we start with the 4-tap mode equations to
+ * compute an approximation of the ratio, and switch to the 7-tap mode equations
+ * if the approximation is higher than the ratio threshold.
+ *
+ * As the 7-tap mode equations will return a ratio smaller than or equal to the
+ * 4-tap mode equations, the resulting ratio could become lower than or equal to
+ * the ratio threshold. This 'equations loop' isn't an issue as long as the
+ * correct equations are used to compute the final input size. Starting with the
+ * 4-tap mode equations ensure that, in case of values resulting in a 'ratio
+ * loop', the smallest of the ratio values will be used, never exceeding the
+ * requested input size.
  *
  * We first clamp the output size according to the hardware capabilitie to avoid
  * auto-cropping the input more than required to satisfy the TRM equations. The
@@ -788,6 +799,9 @@ static void resizer_calc_ratios(struct isp_res_device *res,
 	max_height = min_t(unsigned int, max_height, MAX_OUT_HEIGHT);
 	output->height = clamp(output->height, min_height, max_height);
 
+	ratio->vert = ((input->height - 4) * 256 - 16 - 32 * spv)
+		    / (output->height - 1);
+	if (ratio->vert > MID_RESIZE_VALUE)
 		ratio->vert = ((input->height - 7) * 256 - 32 - 64 * spv)
 			    / (output->height - 1);
 	ratio->vert = clamp_t(unsigned int, ratio->vert,
@@ -856,6 +870,9 @@ static void resizer_calc_ratios(struct isp_res_device *res,
 			      max_width & ~(width_alignment - 1));
 	output->width = ALIGN(output->width, width_alignment);
 
+	ratio->horz = ((input->width - 7) * 256 - 16 - 32 * sph)
+		    / (output->width - 1);
+	if (ratio->horz > MID_RESIZE_VALUE)
 		ratio->horz = ((input->width - 7) * 256 - 32 - 64 * sph)
 			    / (output->width - 1);
 	ratio->horz = clamp_t(unsigned int, ratio->horz,