linux-kernel - Re: [PATCH 06/15] drm/sun4i: tcon: Add support for tcon-top

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Date:   Mon, 21 May 2018 19:27:46 +0200
From:   Jernej Škrabec <jernej.skrabec@...l.net>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     wens@...e.org, robh+dt@...nel.org, mark.rutland@....com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 06/15] drm/sun4i: tcon: Add support for tcon-top

Hi,

Dne ponedeljek, 21. maj 2018 ob 10:07:59 CEST je Maxime Ripard napisal(a):
> On Sat, May 19, 2018 at 08:31:18PM +0200, Jernej Skrabec wrote:
> > If SoC has TCON TOP unit, it has to be configured from TCON, since it
> > has all information needed. Additionally, if it is TCON TV, it must also
> > enable bus gate inside TCON TOP unit.
> 
> Why?

I'll explain my design decision below.

> 
> > Add support for such TCONs.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > ---
> > 
> >  drivers/gpu/drm/sun4i/sun4i_tcon.c | 28 ++++++++++++++++++++++++++++
> >  drivers/gpu/drm/sun4i/sun4i_tcon.h |  8 ++++++++
> >  2 files changed, 36 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > b/drivers/gpu/drm/sun4i/sun4i_tcon.c index 08747fc3ee71..e0c562ce1c22
> > 100644
> > --- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > +++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
> > @@ -688,6 +688,16 @@ static int sun4i_tcon_init_clocks(struct device *dev,
> > 
> >  		dev_err(dev, "Couldn't get the TCON bus clock\n");
> >  		return PTR_ERR(tcon->clk);
> >  	
> >  	}
> > 
> > +
> > +	if (tcon->quirks->needs_tcon_top && tcon->quirks->has_channel_1) {
> > +		tcon->top_clk = devm_clk_get(dev, "tcon-top");
> > +		if (IS_ERR(tcon->top_clk)) {
> > +			dev_err(dev, "Couldn't get the TCON TOP bus clock\n");
> > +			return PTR_ERR(tcon->top_clk);
> > +		}
> > +		clk_prepare_enable(tcon->top_clk);
> > +	}
> > +
> > 
> >  	clk_prepare_enable(tcon->clk);
> >  	
> >  	if (tcon->quirks->has_channel_0) {
> > 
> > @@ -712,6 +722,7 @@ static int sun4i_tcon_init_clocks(struct device *dev,
> > 
> >  static void sun4i_tcon_free_clocks(struct sun4i_tcon *tcon)
> >  {
> >  
> >  	clk_disable_unprepare(tcon->clk);
> > 
> > +	clk_disable_unprepare(tcon->top_clk);
> > 
> >  }
> >  
> >  static int sun4i_tcon_init_irq(struct device *dev,
> > 
> > @@ -980,6 +991,23 @@ static int sun4i_tcon_bind(struct device *dev, struct
> > device *master,> 
> >  	tcon->id = engine->id;
> >  	tcon->quirks = of_device_get_match_data(dev);
> > 
> > +	if (tcon->quirks->needs_tcon_top) {
> > +		struct device_node *np;
> > +
> > +		np = of_parse_phandle(dev->of_node, "allwinner,tcon-top", 0);
> > +		if (np) {
> > +			struct platform_device *pdev;
> > +
> > +			pdev = of_find_device_by_node(np);
> > +			if (pdev)
> > +				tcon->tcon_top = platform_get_drvdata(pdev);
> > +			of_node_put(np);
> > +
> > +			if (!tcon->tcon_top)
> > +				return -EPROBE_DEFER;
> > +		}
> > +	}
> > +
> 
> I might have missed it, but I've not seen the bindings additions for
> that property. This shouldn't really be done that way anyway, instead
> of using a direct phandle, you should be using the of-graph, with the
> TCON-top sitting where it belongs in the flow of data.

Just to answer to the first question, it did describe it in "[PATCH 07/15] dt-
bindings: display: sun4i-drm: Add R40 HDMI pipeline".

As why I designed it that way - HW representation could be described that way 
(ASCII art makes sense when fixed width font is used to view it):

                            / LCD0/LVDS0
                / TCON-LCD0
                |           \ MIPI DSI
mixer0          |
       \        / TCON-LCD1 - LCD1/LVDS1
        TCON-TOP
       /        \ TCON-TV0 - TVE0/RGB
mixer1          |          \
                |           TCON-TOP - HDMI
                |          /
                \ TCON-TV1 - TVE1/RGB

This is a bit simplified, since there is also TVE-TOP, which is responsible 
for sharing 4 DACs between both TVE encoders. You can have two TV outs (PAL/
NTSC) or TVE0 as TV out and TVE1 as RGB or vice versa. It even seems that you 
can arbitrarly choose which DAC is responsible for which signal, so there is a 
ton of possible end combinations, but I'm not 100% sure.

Even though I wrote TCON-TOP twice, this is same unit in HW. R40 manual 
suggest more possibilities, although some of them seem wrong, like RGB feeding 
from LCD TCON. That is confirmed to be wrong when checking BSP code. 

Additionally, TCON-TOP comes in the middle of TVE0 and LCD0, TVE1 and LCD1 for 
pin muxing, although I'm not sure why is that needed at all, since according 
to R40 datasheet, TVE0 and TVE1 pins are dedicated and not on PORT D and PORT 
H, respectively, as TCON-TOP documentation suggest. However, HSYNC and PSYNC 
lines might be shared between TVE (when it works in RGB mode) and LCD. But 
that is just my guess since I'm not really familiar with RGB and LCD 
interfaces.

I'm really not sure what would be the best representation in OF-graph. Can you 
suggest one?

On the other hand, mux callback in TCON driver has all available informations 
at hand. It knows mixer ID, TCON ID and most importantly, encoder type. Based 
on all that informations, it's easy to configure TCON TOP.

I hope you understand. If you have better idea, I'm all ears, since phandle 
seems a bit weird to me too, but I think it's the only future proof, when 
adding LVDS, RGB, TVE or LCD support.

Best regards,
Jernej