linux-kernel - Re: [PATCH v5 07/17] drm/sun4i: sun6i_mipi_dsi: Refactor vertical video start delay

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Date:   Thu, 13 Dec 2018 01:13:40 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        linux-amarula@...rulasolutions.com
Subject: Re: [PATCH v5 07/17] drm/sun4i: sun6i_mipi_dsi: Refactor vertical
 video start delay

Hi Maxime,

On Tue, Dec 11, 2018 at 10:30 PM Jagan Teki <jagan@...rulasolutions.com> wrote:
>
> On Tue, Dec 11, 2018 at 10:19 PM Maxime Ripard
> <maxime.ripard@...tlin.com> wrote:
> >
> > On Mon, Dec 10, 2018 at 09:47:19PM +0530, Jagan Teki wrote:
> > > Video start delay can be computed by subtracting total vertical
> > > timing with front porch timing and with adding 1 delay line for TCON.
> > >
> > > BSP code form BPI-M64-bsp is computing video start delay as
> > > (from linux-sunxi/
> > > drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > >
> > > u32 vfp = panel->lcd_vt - panel->lcd_y - panel->lcd_vbp;
> > > => (panel->lcd_vt) - panel->lcd_y - (panel->lcd_vbp)
> > > => (timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y)
> > >    - panel->lcd_y - (panel->lcd_vbp)
> > > => timmings->ver_front_porch + panel->lcd_vbp + panel->lcd_y
> > >                            - panel->lcd_y - panel->lcd_vbp
> > > => timmings->ver_front_porch
> > >
> > > So, update the start delay computation accordingly.
> > >
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> >
> > Even though it's a bit better now on my A33 board and I don't have the
> > white stripes on the bottom of the display, there's still some
> > flickering with your patches applied.
> >
> > Bisecting it seems to point at that patch, but reverting it doesn't
> > make the issue go away, so it's not really clear which one exactly is
> > at fault.
> >
> > So, just like I asked in your v4, twice,
> >
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2018-November/615339.html
>
> I don't know how can I comment here. Not quite clearly understand your
> setup, because I have verified 3 different panels from different
> vendors one with 2-lane, another with 4-lane and one with video format
> and another one is burstmode format. I even verified with the clock
> rate and register details.
>
> Please suggest me, what can look further on this.

>From the BSP point-of-view I couldn't find have any difference in
start_delay computation between A64, and A33[1]. In fact the driver
initialization code is same, here is A64 dsi driver[2].

1) The only difference that I observe is dsi_gen_wr in BSP [3], the
A33 is right shifting message tx length to 0, 8 for first and next
packet where as A64 did the same by adding +1 before.  Please try to
check that If your panel is using long write.  and
2) Also every dsi transaction in A33 occupy some delay code in
dsi_gen_wr[4], please check the same. and
3) Also If possible please check your panel timings or initialization
sequence, because I don't have any panel with A33.
4) other than these I have didn't notice any differences atleast from
my knowledge, Please suggest me where can I look further.

[1] https://github.com/BPI-SINOVOIP/BPI-M2M-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp/de/lowlevel_sun8iw5/de_dsi.c#L813
[2] https://github.com/BPI-SINOVOIP/BPI-M64-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c
[3] https://github.com/BPI-SINOVOIP/BPI-M2M-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp/de/lowlevel_sun8iw5/de_dsi.c#L402
[4] https://github.com/BPI-SINOVOIP/BPI-M2M-bsp/blob/master/linux-sunxi/drivers/video/sunxi/disp/de/lowlevel_sun8iw5/de_dsi.c#L378