[PATCH v4 10/26] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay

[Jagan Teki <jagan-dyjBcgdgk7Pe9wHmmfpqLFaTQe2KTcn/@public.gmane.org>]

Video start delay can be computed by subtracting total vertical
timing with front porch timing and with adding 1 delay line for TCON.

BSP code form BPI-M64-bsp is computing video start delay as
(from linux-sunxi/
drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)

u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp;
=> (panel->lcd_vt) - panel->lcd_y - (panel->lcd_vbp)
=> (timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y)
   - panel->lcd_y - (panel->lcd_vbp)
=> timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y
  			     - panel->lcd_y - panel->lcd_vbp
=> timmings->ver_front_porch

So, update the start delay computation accordingly.

Signed-off-by: Jagan Teki <jagan-dyjBcgdgk7Pe9wHmmfpqLFaTQe2KTcn/@public.gmane.org>
---
 drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
index fc4252d96c38..f6e3df8d2490 100644
--- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
+++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
@@ -358,7 +358,17 @@ static void sun6i_dsi_inst_init(struct sun6i_dsi *dsi,
 static u16 sun6i_dsi_get_video_start_delay(struct sun6i_dsi *dsi,
 					   struct drm_display_mode *mode)
 {
-	return mode->vtotal - (mode->vsync_end - mode->vdisplay) + 1;
+	u32 vfp = mode->vsync_start - mode->vdisplay;
+	u32 start_delay;
+
+	start_delay = mode->vtotal - vfp + 1;
+	if (start_delay > mode->vtotal)
+		start_delay -= mode->vtotal;
+
+	if (!start_delay)
+		start_delay = 1;
+
+	return start_delay;
 }
 
 static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
-- 
2.18.0.321.gffc6fa0e3