linux-kernel - Re: [PATCH 07/12] drm/sun4i: sun6i_mipi

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Date:   Tue, 2 Oct 2018 15:20:08 +0200
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 07/12] drm/sun4i: sun6i_mipi_dsi: Fix TCON DRQ set bits

On Thu, Sep 27, 2018 at 11:15:50PM +0530, Jagan Teki wrote:
> On Thu, Sep 27, 2018 at 10:28 PM Maxime Ripard
> <maxime.ripard@...tlin.com> wrote:
> >
> > On Thu, Sep 27, 2018 at 05:18:45PM +0530, Jagan Teki wrote:
> > > TCON DRQ set bits for non-burst DSI mode can computed via
> > > horizontal front porch instead of front porch + sync timings.
> > >
> > > Since there no documentation for TCON_DRQ_REG(0x7c) register
> > > this change is taken as reference from BPI-M64-bsp.
> >
> > Detailing more what the issue is would be great.
> >
> > > Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > index 599284971ab6..9918fdb990ff 100644
> > > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > > @@ -367,9 +367,9 @@ static void sun6i_dsi_setup_burst(struct sun6i_dsi *dsi,
> > >       struct mipi_dsi_device *device = dsi->device;
> > >       u32 val = 0;
> >
> > The computation here is in the A64 driver:
> >
> > if ((panel->lcd_ht - panel->lcd_x - panel->lcd_hbp) < 21) {
> >         dsi_dev[sel]->dsi_tcon_drq.bits.drq_mode = 0;
> > } else {
> >         dsi_dev[sel]->dsi_tcon_drq.bits.drq_set =
> >                 (panel->lcd_ht-panel->lcd_x-panel->lcd_hbp-20) *
> >                 dsi_pixel_bits[panel->lcd_dsi_format]/(8*4);
> > }
> >
> > It is testing that the sync + front porch is smaller than 21, and
> > otherwise sets the drq.
> >
> > > -     if ((mode->hsync_end - mode->hdisplay) > 20) {
> >
> > My code here is testing that the difference between hsync_end and
> > hdisplay is superior to 20, and sets the DRQ if true. The condition is
> > reversed, but otherwise, that difference is the front porch plus the
> > sync length.
> 
> True, I understand this, but does drq setting here is specific to SoC?
> I thought of finding DRQ in A31 BSP but I couldn't find the code. do
> you have bsp somewhere in github?
> 
> >
> > > +     if ((mode->hsync_start - mode->hdisplay) > 20) {
> >
> > However, you are testing for just the front porch, unlike what your
> > commit log is saying, and unlike what allwinner's code is saying. So
> > this deserves some explanation.
> 
> but A64 is doing this, do you think it's completely A64 specific or
> testing panel with front porch drq?

See the above code excerpt:
panel->lcd_ht - panel->lcd_x - panel->lcd_hbp

This is hsync + front porch. Not the sole front porch. So no, it's not
doing this.

Maxime


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

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