Re: [linux-sunxi] Re: [PATCH 08/12] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay

[Jagan Teki]

On Saturday 29 September 2018 08:57 PM, Maxime Ripard wrote:
> On Thu, Sep 27, 2018 at 11:03:19PM +0530, Jagan Teki wrote:
> > On Thu, Sep 27, 2018 at 10:44 PM Maxime Ripard
> > <maxime.ripard@xxxxxxxxxxx> wrote:
> > > 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.
> >
> > The current code
> > return mode->vtotal - (mode->vsync_end - mode->vdisplay) + 1;
> >
> > (mode->vsync_end - mode->vdisplay) = front porch + sync
> >
> > but I'm updating here only front porch.
> >
> > > > 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@xxxxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >   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;
> >
> > let me explain this.
> >
> > Actual code from Allwinner
> > u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp;
> >
> > So,
> >
> > => (panel->lcd_vt - panel->lcd_y) - (panel->lcd_vbp)
> > => (front porch + sync + back porch) - (back porch + sync)
>
> Unless Allwinner is doing something fishy, in which case that should
> be mentionned, the back porch doesn't contain the sync pulse.

As per as I understand panel->lcd_vbp is not back porch timings value 
which i used by drm. It is BSP DTS property value and actual back porch 
is calculated as "panel->lcd_vbp - panel->sync"

timmings->ver_sync_time= panel_info->lcd_vspw;
timmings->ver_back_porch= panel_info->lcd_vbp-panel_info->lcd_vspw;