linux-kernel - Re: [PATCH v3 14/21] drm/sun4i: tcon: multiply the vtotal when not in interlace

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Date:   Thu, 18 May 2017 09:51:21 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v3 14/21] drm/sun4i: tcon: multiply the vtotal when not
 in interlace

On Wed, May 17, 2017 at 05:50:45PM +0800, Chen-Yu Tsai wrote:
> On Wed, May 17, 2017 at 3:40 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > It appears that the total vertical resolution needs to be doubled when
> > we're not in interlaced. Make sure that is the case.
> >
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun4i_tcon.c | 25 +++++++++++++++++++++----
> >  1 file changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > index 62e254aedb57..a0f9a8a516c7 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > @@ -153,7 +153,7 @@ static int sun4i_tcon_get_clk_delay(struct drm_display_mode *mode,
> >  void sun4i_tcon0_mode_set(struct sun4i_tcon *tcon,
> >                           struct drm_display_mode *mode)
> >  {
> > -       unsigned int bp, hsync, vsync;
> > +       unsigned int bp, hsync, vsync, vtotal;
> >         u8 clk_delay;
> >         u32 val = 0;
> >
> > @@ -192,9 +192,26 @@ void sun4i_tcon0_mode_set(struct sun4i_tcon *tcon,
> >         DRM_DEBUG_DRIVER("Setting vertical total %d, backporch %d\n",
> >                          mode->crtc_vtotal, bp);
> >
> > +       /*
> > +        * The vertical resolution needs to be doubled in all
> > +        * cases. We could use crtc_vtotal and always multiply by two,
> > +        * but that leads to a rounding error in interlace when vtotal
> > +        * is odd.
> > +        *
> > +        * This happens with TV's PAL for example, where vtotal will
> > +        * be 625, crtc_vtotal 312, and thus crtc_vtotal * 2 will be
> > +        * 624, which apparently confuses the hardware.
> > +        *
> > +        * To work around this, we will always use vtotal, and
> > +        * multiply by two only if we're not in interlace.
> > +        */
> > +       vtotal = mode->vtotal;
> > +       if (!(mode->flags & DRM_MODE_FLAG_INTERLACE))
> > +               vtotal = vtotal * 2;
> > +
> >         /* Set vertical display timings */
> >         regmap_write(tcon->regs, SUN4I_TCON0_BASIC2_REG,
> > -                    SUN4I_TCON0_BASIC2_V_TOTAL(mode->crtc_vtotal * 2) |
> > +                    SUN4I_TCON0_BASIC2_V_TOTAL(vtotal) |
> >                      SUN4I_TCON0_BASIC2_V_BACKPORCH(bp));
> >
> >         /* Set Hsync and Vsync length */
> > @@ -279,9 +296,9 @@ void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
> >         /* Set vertical display timings */
> >         bp = mode->crtc_vtotal - mode->crtc_vsync_start;
> >         DRM_DEBUG_DRIVER("Setting vertical total %d, backporch %d\n",
> > -                        mode->vtotal, bp);
> > +                        mode->crtc_vtotal, bp);
> 
> You should duplicate the logic from channel 0 to channel 1.
> In fact, interlaced modes happen predominantly on channel 1,
> for composite and HDMI modes.

Gaah, you're right, this was obviously meant for the channel 1.. I'll
resend.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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