drm/radeon: fix interlaced modes on DCE8

commit 77ae5f4b upstream.

Need to double the viewport height.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -1405,6 +1405,9 @@ static int dce4_crtc_do_set_base(struct drm_crtc *crtc,
 	       (x << 16) | y);
 	viewport_w = crtc->mode.hdisplay;
 	viewport_h = (crtc->mode.vdisplay + 1) & ~1;
+	if ((rdev->family >= CHIP_BONAIRE) &&
+	    (crtc->mode.flags & DRM_MODE_FLAG_INTERLACE))
+		viewport_h *= 2;
 	WREG32(EVERGREEN_VIEWPORT_SIZE + radeon_crtc->crtc_offset,
 	       (viewport_w << 16) | viewport_h);