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

[Jagan Teki]

On 20/11/18 9:55 PM, Jagan Teki wrote:
> On Tue, Nov 20, 2018 at 9:27 PM Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote:
> > On Thu, Nov 15, 2018 at 11:19:53PM +0530, Jagan Teki wrote:
> > > 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.
> >
> > Not even the timings? How did you get that information then?
>
> datasheet has timing values, but this changes need controller
> information about VBP register that I don't have. But again existing
> VBP is not back porch for real, it's front porch.

I'm about to send next version by combining with burst mode changes in
one series. Do you have any further inputs on this. I didn't not see
any breakage with 4-lane devices, but has issue with 2-lane w/o this change.