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

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Message-ID: <20190107141158.zaimizk4rlqa6xli@flea>
Date:   Mon, 7 Jan 2019 15:11:58 +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 <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

On Fri, Dec 21, 2018 at 02:26:11AM +0530, Jagan Teki 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.
> 
> Is reverting this patch, work fine or not?

As I was saying, it doesn't.

> This patch is trying to make use of front porch instead of existing
> back porch to compute the delay. Since we revert the VBP fix patch[1]
> to assume VBP as VFP value look like your setup would also require to
> revert this change. But as per BSP or drm_mode details all of my
> displays even work with and w/o reverting these two.

Again, I cannot help you without the datasheet for the panels you're
trying to submit.

Maxime

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

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