Hi, On Mon, 2019-02-11 at 15:41 +0100, Maxime Ripard wrote: > The current calculation for the video start delay in the current DSI driver > is that it is the total vertical size, minus the front porch and sync length, > plus 1. This equals to the active vertical size plus the back porch plus 1. > > That 1 is coming in the Allwinner BSP from an variable that is set to 1. > However, if we look at the Allwinner BSP more closely, and especially in > the "legacy" code for the display (in drivers/video/sunxi/legacy/), we can > see that this variable is actually computed from the porches and the sync > minus 10, clamped between 8 and 100. For future reference, it look like there is a version of the BSP where this is clamped between 8 and 31 in the legacy ebios code: https://github.com/Icenowy/linux-kernel-lichee-a33/blob/master/drivers/video/sunxi/legacy/disp/de_bsp/de/ebios/de_dsi.c#L687 As well as in the A23 code: https://github.com/Icenowy/linux-kernel-lichee-a33/blob/master/drivers/video/sunxi/disp/de/lowlevel_sun8iw3/de_dsi.c#L686 > This fixes the start delay symptom we've seen on some panels (vblank > timeouts with vertical white stripes at the bottom of the panel). > > Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx> > --- > drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c > index 380fc527a707..9471fa695ec7 100644 > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c > @@ -357,7 +357,9 @@ 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; > + u16 start = clamp(mode->vtotal - mode->vdisplay - 10, 8, 100); > + > + return mode->vtotal - (mode->vsync_end - mode->vdisplay) + start; Looking at the formula from the BSP, I get a different result from yours. >From what I can see, the BSP formula is: start_delay = vtotal - vfp + start vfp = vtotal - y - vbp With vbp counting the back porch and sync length. So the final value can be simplified: start_delay = vbp + y + start Translated to DRM: start_delay = vtotal - vsync_start + vdisplay + start Which differs from your formula by the sync length. Does this also work out for your hardware? I guess it's best to stick close to the BSP if we can. Cheers, Paul > } > > static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi, -- Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
