On Thu, Sep 27, 2018 at 10:44 PM Maxime Ripard
[off-list ref] wrote:

On Thu, Sep 27, 2018 at 05:18:46PM +0530, Jagan Teki wrote:

quoted

Accordingly to BPI-M64-bsp DE DSI code Video start delay
can be computed by subtracting total vertical timing with
front porch timing and with adding 1 delay line for TCON.

This is what the current code is doing as well.

The current code
return mode->vtotal - (mode->vsync_end - mode->vdisplay) + 1;

(mode->vsync_end - mode->vdisplay) = front porch + sync

but I'm updating here only front porch.

quoted

This patch simply add the start_delay logic from BPI-M64-bsp,
w/o this new computation, the DSI on A64 encounter vblank time out.

[CRTC:36:crtc-0] vblank wait timed out

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
---
 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 9918fdb990ff..217db74c6dc3 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;

let me explain this.

Actual code from Allwinner
u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp;

So,

=> (panel->lcd_vt - panel->lcd_y) - (panel->lcd_vbp)
=> (front porch + sync + back porch) - (back porch + sync)
=> front porch + sync + back porch - back porch - sync
=> front porch
=> mode->vsync_start - mode->vdisplay

Hope it clear.