linux-kernel - Re: [PATCH v2 01/12] drm/sun4i: sun6i_mipi_dsi: Compute burst mode loop N1 instruction delay

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Date:   Tue, 20 Nov 2018 08:01:36 -0800
From:   Vasily Khoruzhick <anarsoul@...il.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Jagan Teki <jagan@...rulasolutions.com>,
        maarten.lankhorst@...ux.intel.com, sean@...rly.run,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        thierry.reding@...il.com, Mark Rutland <mark.rutland@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        arm-linux <linux-arm-kernel@...ts.infradead.org>,
        Michael Nazzareno Trimarchi <michael@...rulasolutions.com>,
        TL Lim <tllim@...e64.org>, linux-sunxi@...glegroups.com,
        linux-amarula@...rulasolutions.com
Subject: Re: [PATCH v2 01/12] drm/sun4i: sun6i_mipi_dsi: Compute burst mode
 loop N1 instruction delay

On Tue, Nov 20, 2018 at 7:59 AM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Tue, Nov 20, 2018 at 07:06:30PM +0530, Jagan Teki wrote:
> > On Tue, Nov 20, 2018 at 6:53 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > >
> > > On Mon, Nov 19, 2018 at 04:28:29PM +0530, Jagan Teki wrote:
> > > > On Mon, Nov 19, 2018 at 1:57 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
> > > > >
> > > > > On Fri, Nov 16, 2018 at 10:09:05PM +0530, Jagan Teki wrote:
> > > > > > Loop N1 instruction delay for burst mode lcd panel are
> > > > > > computed as per BSP code.
> > > > > >
> > > > > > Reference code is available in BSP (from linux-sunxi
> > > > > > drivers/video/sunxi/disp2/disp/de/lowlevel_sun50iw1/de_dsi.c)
> > > > > >
> > > > > > dsi_dev[sel]->dsi_inst_loop_num.bits.loop_n1=
> > > > > > (panel->lcd_ht-panel->lcd_x)*(150)/(panel->lcd_dclk_freq*8) - 50;
> > > > > > => (((mode->htotal - mode->hdisplay) * 150) /
> > > > > >      ((mode->clock / 1000) * 8)) - 50;
> > > > > >
> > > > > > So use the similar computation for loop N1 delay.
> > > > > >
> > > > > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > > >
> > > > > *why* are you doing this? What is it fixing? on which devices?
> > > >
> > > > You mentioned the separate function to compute the delay for all modes
> > > > [1], ie what I did. did I missing anything?
> > >
> > > You're missing that you are never explaining why that patch is needed
> > > in the first place. Or answering the question I asked a couple of
> > > lines above.
> >
> > OK.
> >
> > The instruction delay varies between video and burst mode. for burst
> > mode panels it is computed based on the panel clock along with
> > horizontal sync+porch timings.
>
> You're still stating a fact. What issue, that you experienced, are you
> trying to solve here?

IIRC that's what BSP driver does. Otherwise panels that use burst mode
just don't work.

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