Re: [linux-sunxi] Re: [PATCH 06/12] drm/sun4i: sun6i_mipi_dsi: Fix VBP size calculation

[Jagan Teki]

On Saturday 29 September 2018 07:23 PM, Maxime Ripard wrote:
> On Thu, Sep 27, 2018 at 09:50:34PM +0530, Jagan Teki wrote:
> > On Thu, Sep 27, 2018 at 8:51 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
> > > On Thu, Sep 27, 2018 at 05:18:44PM +0530, Jagan Teki wrote:
> > > > According to horizontal and vertical timings are defined
> > > > per the diagram from include/drm/drm_modes.h
> > > >
> > > > Back porch = [hv]total - [hv]sync_end
> > > >
> > > > So, update SUN6I_DSI_BASIC_SIZE0_VBP calculation as
> > > > mode->vtotal - mode->vsync_end
> > > >
> > > > Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >   drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
> > > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > index 1c7e42015645..599284971ab6 100644
> > > > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > > @@ -526,8 +526,8 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi,
> > > >        regmap_write(dsi->regs, SUN6I_DSI_BASIC_SIZE0_REG,
> > > >                     SUN6I_DSI_BASIC_SIZE0_VSA(mode->vsync_end -
> > > >                                               mode->vsync_start) |
> > > > -                  SUN6I_DSI_BASIC_SIZE0_VBP(mode->vsync_start -
> > > > -                                            mode->vdisplay));
> > > > +                  SUN6I_DSI_BASIC_SIZE0_VBP(mode->vtotal -
> > > > +                                            mode->vsync_end));
> > >
> > > Is it purely theoretical, or did you find some source that back that?
> >
> > VSA is done as per that, sync_end - sync start would give sync time.
>
> That's a different register though.
>
> > VBP also done in BPI-M64-bsp[1] which results back porch existing code
> > results fron porch.
> >
> > [1] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c#L955
>
> That code does back porch - sync length. Such a calculation doesn't
> make much sense as is, but you're saying that it results in the front
> porch. Again, what makes you say that?

No what code shows is not a real back porch value used for drm it's 
panel back porch value which is a DTS property in BSP.
(I made wrong comment on previous mail as front porch, sorry)

here is the real code

from drivers/video/sunxi/disp2/disp/de/disp_lcd.c
timmings->ver_sync_time= panel_info->lcd_vspw;
timmings->ver_back_porch= panel_info->lcd_vbp-panel_info->lcd_vspw;


u32 vbp = panel->lcd_vbp;
u32 vspw = panel->lcd_vspw;
dsi_dev[sel]->dsi_basic_size0.bits.vbp = vbp-vspw;

So,

dsi_dev[sel]->dsi_basic_size0.bits.vbp = panel->lcd_vbp - panel->lcd_vspw;

=>  timmings->ver_back_porch + panel_info->lcd_vspw - panel_info->lcd_vspw
=>  timmings->ver_back_porch
=>  mode->vtotal - mode->end

VSA, which a proper value.

dsi_dev[sel]->dsi_basic_size0.bits.vsa = vspw;
=> panel_info->lcd_vspw;
=> timmings->ver_sync_time
=> mode->vsync_end - mode->vsync_start