Messages in this thread | | | Date | Thu, 27 Sep 2018 19:14:51 +0200 | From | Maxime Ripard <> | Subject | Re: [PATCH 08/12] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay |
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On Thu, Sep 27, 2018 at 05:18:46PM +0530, Jagan Teki wrote: > 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.
> 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;
Again, this is wrong and contrary to what your commit log is saying.
The Allwinner code has:
u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp; u32 dsi_start_delay = panel->lcd_vt - vfp + 1;
So, essentially:
vtotal - (vtotal - vdisplay - back porch) + 1
The backporch is hsync_total - hsync_end, so we end up, removing the addition / removal of vtotal, with:
vdisplay - (vsync_total - vsync_end) + 1
The formula used there looks indeed different, but unlike what you were saying.
> + u32 start_delay; > + > + start_delay = mode->vtotal - vfp + 1; > + if (start_delay > mode->vtotal) > + start_delay -= mode->vtotal; > + > + if (!start_delay) > + start_delay = 1; > +
I guess that it's actually the clamping that fixes thing. It should be mentionned in your commit log.
Maxime
-- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
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