staging: rpivid: Align column strides based on optimal SDRAM pages

There is a small performance gain by having the column strides
aligned to SDRAM banks.
Precompute the column heights that would follow from various common
image heights, and align to the nearest one of them.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

drivers/staging/media/rpivid/rpivid_video.c

@@ -107,13 +107,31 @@ void rpivid_prepare_src_format(struct v4l2_pix_format_mplane *pix_fmt)
 	pix_fmt->plane_fmt[0].sizeimage = size;
 }
 
+/*
+ * NB This list MUST match the aligned heights advertised by the DRM driver
+ * if anything in the path validates the DRM modifier against those advertised.
+ */
+static unsigned int page_aligned_heights[] = {
+	208,	/* 120 lines */
+	400,	/* 240 lines */
+	624,	/* 360 lines */
+	752,	/* 480 lines */
+	880,	/* 576 lines */
+	1136,	/* 720 lines */
+	1648,	/* 1080 lines */
+	2192,	/* 1440 lines */
+	3280,	/* 2160 lines */
+	0
+};
+
 /* Take any pix_format and make it valid */
 static void rpivid_prepare_dst_format(struct v4l2_pix_format_mplane *pix_fmt)
 {
 	unsigned int width = pix_fmt->width;
 	unsigned int height = pix_fmt->height;
 	unsigned int sizeimage = pix_fmt->plane_fmt[0].sizeimage;
 	unsigned int bytesperline = pix_fmt->plane_fmt[0].bytesperline;
+	int i;
 
 	if (!width)
 		width = RPIVID_DEFAULT_WIDTH;
@@ -133,12 +151,20 @@ static void rpivid_prepare_dst_format(struct v4l2_pix_format_mplane *pix_fmt)
 		/* Width rounds up to columns */
 		width = ALIGN(width, 128);
 
-		/* 16 aligned height - not sure we even need that */
-		height = ALIGN(height, 16);
+		/* 2 aligned height - as it will be YUV420 */
+		height = ALIGN(height, 2);
+
 		/* column height
 		 * Accept suggested shape if at least min & < 2 * min
 		 */
-		bytesperline = constrain2x(bytesperline, height * 3 / 2);
+		for (i = 0; page_aligned_heights[i]; i++) {
+			if (page_aligned_heights[i] > (height * 3) / 2) {
+				bytesperline = page_aligned_heights[i];
+				break;
+			}
+		}
+
+		bytesperline = constrain2x(pix_fmt->plane_fmt[0].bytesperline, bytesperline);
 
 		/* image size
 		 * Again allow plausible variation in case added padding is
@@ -153,13 +179,20 @@ static void rpivid_prepare_dst_format(struct v4l2_pix_format_mplane *pix_fmt)
 		 */
 		width = ALIGN(((width + 2) / 3), 32) * 3;
 
-		/* 16-aligned height. */
-		height = ALIGN(height, 16);
+		/* 2 aligned height - as it will be YUV420 */
+		height = ALIGN(height, 2);
 
 		/* column height
 		 * Accept suggested shape if at least min & < 2 * min
 		 */
-		bytesperline = constrain2x(bytesperline, height * 3 / 2);
+		for (i = 0; page_aligned_heights[i]; i++) {
+			if (page_aligned_heights[i] > (height * 3) / 2) {
+				bytesperline = page_aligned_heights[i];
+				break;
+			}
+		}
+
+		bytesperline = constrain2x(pix_fmt->plane_fmt[0].bytesperline, bytesperline);
 
 		/* image size
 		 * Again allow plausible variation in case added padding is