drm/vc4: Use the TPZ scaling filter for 1x1 source images

The documentation says that the TPZ filter can not upscale,
and requesting a scaling factor > 1:1 will output the original
image in the top left, and repeat the right/bottom most pixels
thereafter.
That fits perfectly with upscaling a 1x1 image which is done
a fair amount by some compositors to give solid colour, and it
saves a large amount of LBM (TPZ is based on src size, whilst
PPF is based on dest size).

Select TPZ filter for images with source rectangle <=1.

Signed-off-by: Dave Stevenson <[email protected]>

drivers/gpu/drm/vc4/vc4_plane.c

@@ -265,7 +265,11 @@ static enum vc4_scaling_mode vc4_get_scaling_mode(u32 src, u32 dst)
 {
 	if (dst == src >> 16)
 		return VC4_SCALING_NONE;
-	if (3 * dst >= 2 * (src >> 16))
+
+	if (src <= (1 << 16))
+		/* Source rectangle <= 1 pixel can use TPZ for resize/upscale */
+		return VC4_SCALING_TPZ;
+	else if (3 * dst >= 2 * (src >> 16))
 		return VC4_SCALING_PPF;
 	else
 		return VC4_SCALING_TPZ;