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

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Mon, Mar 11, 2019 at 09:31:11PM +0530, Jagan Teki wrote:
> 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

You're answering one out of three questions.

> > > 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]

You're still answering partially here. Those timings are working for
RGB, you have no proof that we need to make the same adjustments for
DSI.

> > > 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]

It doesn't matter where you took it from. If you cannot explain what
happen, putting a random label that doesn't explain anything will not
help.

Maxime

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

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