Re: [PATCH v4 08/26] drm/sun4i: sun6i_mipi_dsi: Fix VBP size calculation

[Jagan Teki]

On Thu, Nov 15, 2018 at 3:26 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
>
> Hi,
>
> On Tue, Nov 13, 2018 at 04:46:15PM +0530, Jagan Teki wrote:
> > The horizontal and vertical back porch calculation in BSP
> > code is simply following the Linux drm comment diagram, in
> > include/drm/drm_modes.h which is
> >
> > [hv]back porch = [hv]total - [hv]sync_end
> >
> > BSP code form BPI-M64-bsp is calculating vertical back porch as
> > (from linux-sunxi/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;
> >
> > vbp = panel->lcd_vbp;
> > vspw = panel->lcd_vspw;
> > dsi_dev[sel]->dsi_basic_size0.bits.vbp = vbp-vspw;
> > 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
> >
> > Which evatually same as mode->vtotal - mode->vsync_end so update the
> > same in SUN6I_DSI_BASIC_SIZE0_VBP
> >
> > On the information note, existing SUN6I_DSI_BASIC_SIZE0_VSA is proper
> > value.
> >
> > Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
>
> I've tested your changes on my A33 board, and this commit will break
> it.
>
> It creates vblank timeouts, and visual artifacts at the bottom of the
> display.

Strange, VBP is earlier gives front porch which is anyway wrong.

>
> Later commits seem to fix the issue, but will create some blanking on
> the upper third of the display.
>
> Since the documentation is quite sparse, and a MIPI-DSI analyzer is
> way too expensive, I'd really like to have at least what each of these
> commits are actually fixing, and what symptoms each of these were
> causing, and not just "the BSP does it".

W/o this 2-lane panel is breaking, same vblank timeout and visual
artifacts at the bottom of the panel. though the commits may reference
BSP, I have at-least tested on 3 different panels for us to prove its
working.

>
> Having some datasheet for the panels you had working would help too.

Unfortunately datasheet doesn't have any required information what we
actually looking for.