Re: [PATCH v8 01/15] drm/sun4i: dsi: Fix video start delay computation

[Jagan Teki <jagan@amarulasolutions.com>]

On Mon, Mar 11, 2019 at 9:07 PM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
>
> On Mon, Mar 11, 2019 at 07:06:23PM +0530, Jagan Teki wrote:
> > Vertical video start delay is computed by excluding vertical front
> > porch value from total vertical timings.
> >
> > This clearly confirmed from BSP code and here how it computed,
> >
> > (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
> >
> > But the current driver is assuming it can exclude vertical front
> > porch along with vertical sync values from total vertical timings,
> > which resulting wrong start delay indeed wrong picture rendering
> > in the panel.
>
> Same story here: which panel, which datasheet, which "wrong picture
> rendering"?

It's bananapi,s070wv20-ct16 DSI

>
> > Example: timings, where it produces the issue.
> > {
> >       .vdisplay       = 600,
> >       .vsync_start    = 600 + 12,
> >       .vsync_end      = 600 + 12 + 2,
> >       .vtotal         = 600 + 12 + 2 + 21,
> > }
>
> Can you 100% trust those timings?

ie. reason, I have given the Mainline timings [1]. The above timings
are wrongly mentioned actual timings are from [1]

>
> > It produces the desired start delay value as 19 but the correct working
> > value should be 513.
> >
> > So, Fix it by computing proper video start delay.
> >
> > Fixes: 69006ef0ecb1 ("drm/sun4i: dsi: Change the start delay calculation")
> > Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 62a508420227..8d6292c0158b 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -364,8 +364,14 @@ 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)
> >  {
> > -     u16 start = clamp(mode->vtotal - mode->vdisplay - 10, 8, 100);
> > -     u16 delay = mode->vtotal - (mode->vsync_end - mode->vdisplay) + start;
> > +     u16 delay = mode->vtotal - (mode->vsync_start - mode->vdisplay);
> > +
> > +     /**
> > +      * BSP comment:
> > +      * put start_delay to tcon. set ready sync early to dramfreq,
> > +      * so set start_delay 1
> > +      */
>
> That doesn't make any sense to me... What does it mean?

Which is meaning as above stated as "BSP comment" from here[2]

[1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/gpu/drm/panel/panel-simple.c?id=7ad8b41cd8f5c2842646d01cdd576663caee04a7
[2] https://github.com/longsleep/linux-pine64/blob/pine64-hacks-1.2/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L729
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