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

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Message-ID: <20181211164900.wfmkmbrbj3nmlb3h@flea>
Date:   Tue, 11 Dec 2018 17:49:00 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, 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

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

> 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".

Maxime

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

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