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

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Message-ID: <20181120155826.j5rja22jnxpkmjrs@flea>
Date:   Tue, 20 Nov 2018 16:58:26 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <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>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Thierry Reding <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>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Michael 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 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?

Maxime

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

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