On Fri, Dec 21, 2018 at 02:26:11AM +0530, Jagan Teki wrote:

On Tue, Dec 11, 2018 at 10:19 PM Maxime Ripard
[off-list ref] wrote:

quoted

On Mon, Dec 10, 2018 at 09:47:19PM +0530, Jagan Teki wrote:

quoted

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@amarulasolutions.com>

Even though it's a bit better now on my A33 board and I don't have the
white stripes on the bottom of the display, there's still some
flickering with your patches applied.

Bisecting it seems to point at that patch, but reverting it doesn't
make the issue go away, so it's not really clear which one exactly is
at fault.

Is reverting this patch, work fine or not?

As I was saying, it doesn't.

This patch is trying to make use of front porch instead of existing
back porch to compute the delay. Since we revert the VBP fix patch[1]
to assume VBP as VFP value look like your setup would also require to
revert this change. But as per BSP or drm_mode details all of my
displays even work with and w/o reverting these two.

Again, I cannot help you without the datasheet for the panels you're
trying to submit.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com