linux-kernel - Re: [PATCH 10/15] drm/sun4i: tcon: Switch mux on only for composite

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Date:   Thu, 9 Mar 2017 11:58:00 +0100
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>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH 10/15] drm/sun4i: tcon: Switch mux on only for composite

On Wed, Mar 08, 2017 at 11:51:39AM +0800, Chen-Yu Tsai wrote:
> On Tue, Mar 7, 2017 at 4:56 PM, Maxime Ripard
> <maxime.ripard@...e-electrons.com> wrote:
> > Even though that mux is undocumented, it seems like it needs to be set to 1
> > when using composite, and 0 when using HDMI.
> >
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun4i_tcon.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > index d2335f109601..93249c5ab1e4 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > @@ -268,11 +268,16 @@ void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon, struct drm_encoder *encoder,
> >                            SUN4I_TCON_GCTL_IOMAP_MASK,
> >                            SUN4I_TCON_GCTL_IOMAP_TCON1);
> >
> > +       if (encoder->encoder_type == DRM_MODE_ENCODER_TVDAC)
> > +               val = 1;
> > +       else
> > +               val = 0;
> > +
> >         /*
> >          * FIXME: Undocumented bits
> >          */
> >         if (tcon->quirks->has_unknown_mux)
> > -               regmap_write(tcon->regs, SUN4I_TCON_MUX_CTRL_REG, 1);
> > +               regmap_write(tcon->regs, SUN4I_TCON_MUX_CTRL_REG, val);
> 
> We might want to do this the other way around, i.e. exporting
> 
>     int sun4i_tcon_mux_set(struct drm_device *drm, int encoder_type,
>                            int pipeline)
> 
> and have downstream encoders call it. For the A31, the mux is not exclusively
> used for channel 1; there is a mux setting for MIPI DSI as well, but AFAIK
> DSI is connected to channel 0.

We could make it part of sun4i_tcon_channel_enable too, though. What
do you think?

> Additionally, the mux registers are only valid in the first TCON, meaning
> it must available be active in 2 pipeline chips. It's also why we'd pass
> "struct drm_device *" instead of "struct sun4i_tcon *".

Hmmmm. That's going to be tricky to support. Has this been confirmed
somehow? Is the register used for something else on TCON1?

Thanks,
Maxime

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

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