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

[Maxime Ripard]

On Mon, Oct 01, 2018 at 01:25:59PM +0530, Jagan Teki wrote:
> 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;

Then this is what you should have started with in your commit
log. Where is that code coming from? Have you been able to confirm
that with an oscilloscope?

Maxime

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

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