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Date:   Fri, 14 Feb 2020 23:32:31 +0200
From:   Andrey Lebedev <andrey.lebedev@gmail.com>
To:     Maxime Ripard <maxime@cerno.tech>
Cc:     wens@csie.org, airlied@linux.ie, daniel@ffwll.ch,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-sunxi@googlegroups.com, Andrey Lebedev <andrey@lebedev.lt>
Subject: Re: [PATCH v2 2/2] ARM: sun7i: dts: Add LVDS panel support on A20
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On Fri, Feb 14, 2020 at 09:53:51AM +0100, Maxime Ripard wrote:
> On Fri, Feb 14, 2020 at 10:43:58AM +0200, Andrey Lebedev wrote:
> > On Fri, Feb 14, 2020 at 08:52:18AM +0100, Maxime Ripard wrote:
> > > > > This will create a spurious warning message for TCON1, since we
> > > > > adjusted the driver to tell it supports LVDS, but there's no LVDS
> > > > > reset line, so we need to make it finer grained.
> > > >
> > > > Yes, I can attribute two of the messages in my dmesg log [1] to this
> > > > ("Missing LVDS properties" and "LVDS output disabled". "sun4i-tcon
> > > > 1c0d000.lcd-controller" is indeed tcon1). And yes, I can see how they
> > > > can be confusing to someone.
> > > >
> > > > I'd need some pointers on how to deal with that though (if we want to do
> > > > it in this scope).
> > >
> > > Like I was mentionning, you could introduce a new compatible for each
> > > TCON (tcon0 and tcon1) and only set the support_lvds flag for tcon0
> >
> > Can you give me an idea how that compatible might look like?
> >
> > 		tcon0: lcd-controller@1c0c000 {
> > 			compatible = "allwinner,sun7i-a20-tcon", "allwinner,lvds";
> >
> > or
> >
> > 		tcon0: lcd-controller@1c0c000 {
> > 			compatible = "allwinner,sun7i-a20-tcon", "allwinner,tcon0";
> >
> > ? Or something completely different?
> 
> Something like
> 
> &tcon0 {
>     compatible = "allwinner,sun7i-a20-tcon0", "allwinner,sun7i-a20-tcon";
> };
> 
> &tcon1 {
>     compatible = "allwinner,sun7i-a20-tcon1", "allwinner,sun7i-a20-tcon";
> };
> 

Hi Maxime, here is what I came up with, please take a look. If the
approach is right, I'll split it up and include into the patch set.

From f3e45c958a9551a52ac26435785bdb572e54d8db Mon Sep 17 00:00:00 2001
From: Andrey Lebedev <andrey@lebedev.lt>
Date: Fri, 14 Feb 2020 23:21:59 +0200
Subject: [PATCH] Mark tcon0 to be the only tcon capable of LVDS on sun7i-a20

This allows to avoid warnings about reset line not provided for tcon1.

Signed-off-by: Andrey Lebedev <andrey@lebedev.lt>
---
 arch/arm/boot/dts/sun7i-a20.dtsi   |  2 +-
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 22 +++++++++++++++++++++-
 drivers/gpu/drm/sun4i/sun4i_tcon.h |  2 ++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/arm/boot/dts/sun7i-a20.dtsi b/arch/arm/boot/dts/sun7i-a20.dtsi
index 3b3c366a2bee..bab59fc4d9b1 100644
--- a/arch/arm/boot/dts/sun7i-a20.dtsi
+++ b/arch/arm/boot/dts/sun7i-a20.dtsi
@@ -405,7 +405,7 @@
 		};
 
 		tcon0: lcd-controller@1c0c000 {
-			compatible = "allwinner,sun7i-a20-tcon";
+			compatible = "allwinner,sun7i-a20-tcon0", "allwinner,sun7i-a20-tcon";
 			reg = <0x01c0c000 0x1000>;
 			interrupts = <GIC_SPI 44 IRQ_TYPE_LEVEL_HIGH>;
 			resets = <&ccu RST_TCON0>, <&ccu RST_LVDS>;
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 800a9bd86112..cb2040aec436 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -1107,6 +1107,25 @@ static struct sunxi_engine *sun4i_tcon_find_engine(struct sun4i_drv *drv,
 	return sun4i_tcon_find_engine_traverse(drv, node, 0);
 }
 
+/*
+ * Check if given tcon supports LVDS
+ *
+ * Some of the sunxi SoC variants contain several timing controllers, but only
+ * one of them can be used to drive LVDS screen. In this case such tcon is
+ * identified in respective quirks struct: lvds_compatible_tcon property will
+ * hold "compatible" string of the tcon, that supports LVDS.
+ *
+ * If lvds_compatible_tcon is not set, all tcons are considered capable of
+ * driving LVDS.
+ */
+static bool sun4i_tcon_lvds_compat(struct device *dev, struct sun4i_tcon *tcon)
+{
+	if (tcon->quirks->lvds_compatible_tcon == NULL)
+		return true;
+	return of_device_is_compatible(dev->of_node,
+	                               tcon->quirks->lvds_compatible_tcon);
+}
+
 static int sun4i_tcon_bind(struct device *dev, struct device *master,
 			   void *data)
 {
@@ -1161,7 +1180,7 @@ static int sun4i_tcon_bind(struct device *dev, struct device *master,
 		return ret;
 	}
 
-	if (tcon->quirks->supports_lvds) {
+	if (tcon->quirks->supports_lvds && sun4i_tcon_lvds_compat(dev, tcon)) {
 		/*
 		 * This can only be made optional since we've had DT
 		 * nodes without the LVDS reset properties.
@@ -1481,6 +1500,7 @@ static const struct sun4i_tcon_quirks sun6i_a31s_quirks = {
 
 static const struct sun4i_tcon_quirks sun7i_a20_quirks = {
 	.supports_lvds		= true,
+	.lvds_compatible_tcon	= "allwinner,sun7i-a20-tcon0",
 	.has_channel_0		= true,
 	.has_channel_1		= true,
 	.dclk_min_div		= 4,
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index cfbf4e6c1679..bc87d28ee341 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -235,6 +235,8 @@ struct sun4i_tcon_quirks {
 	bool	needs_de_be_mux; /* sun6i needs mux to select backend */
 	bool    needs_edp_reset; /* a80 edp reset needed for tcon0 access */
 	bool	supports_lvds;   /* Does the TCON support an LVDS output? */
+	/* "compatible" string of TCON that exclusively supports LVDS */
+	const char *lvds_compatible_tcon;
 	u8	dclk_min_div;	/* minimum divider for TCON0 DCLK */
 
 	/* callback to handle tcon muxing options */
-- 
2.20.1


-- 
Andrey Lebedev aka -.- . -.. -.. . .-.
Software engineer
Homepage: http://lebedev.lt/