[PATCH v3 2/5] drm/sun4i: tcon: set sync polarity for tcon1 channel

[Jernej Skrabec]

Channel 1 has polarity bits for vsync and hsync signals but driver never
sets them. It turns out that with pre-HDMI2 controllers seemingly there
is no issue if polarity is not set. However, with HDMI2 controllers
(H6) there often comes to de-synchronization due to phase shift. This
causes flickering screen. It's safe to assume that similar issues might
happen also with pre-HDMI2 controllers.

Solve issue with setting vsync and hsync polarity. Note that display
stacks with tcon top have polarity bits actually in tcon0 polarity
register.

Fixes: 9026e0d122ac ("drm: Add Allwinner A10 Display Engine support")
Reviewed-by: Chen-Yu Tsai <wens at csie.org>
Tested-by: Andre Heider <a.heider at gmail.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec at siol.net>
---
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 25 +++++++++++++++++++++++++
 drivers/gpu/drm/sun4i/sun4i_tcon.h |  6 ++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 6b9af4c08cd6..9f06dec0fc61 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -672,6 +672,30 @@ static void sun4i_tcon1_mode_set(struct sun4i_tcon *tcon,
 		     SUN4I_TCON1_BASIC5_V_SYNC(vsync) |
 		     SUN4I_TCON1_BASIC5_H_SYNC(hsync));
 
+	/* Setup the polarity of multiple signals */
+	if (tcon->quirks->polarity_in_ch0) {
+		val = 0;
+
+		if (mode->flags & DRM_MODE_FLAG_PHSYNC)
+			val |= SUN4I_TCON0_IO_POL_HSYNC_POSITIVE;
+
+		if (mode->flags & DRM_MODE_FLAG_PVSYNC)
+			val |= SUN4I_TCON0_IO_POL_VSYNC_POSITIVE;
+
+		regmap_write(tcon->regs, SUN4I_TCON0_IO_POL_REG, val);
+	} else {
+		/* according to vendor driver, this bit must be always set */
+		val = SUN4I_TCON1_IO_POL_UNKNOWN;
+
+		if (mode->flags & DRM_MODE_FLAG_PHSYNC)
+			val |= SUN4I_TCON1_IO_POL_HSYNC_POSITIVE;
+
+		if (mode->flags & DRM_MODE_FLAG_PVSYNC)
+			val |= SUN4I_TCON1_IO_POL_VSYNC_POSITIVE;
+
+		regmap_write(tcon->regs, SUN4I_TCON1_IO_POL_REG, val);
+	}
+
 	/* Map output pins to channel 1 */
 	regmap_update_bits(tcon->regs, SUN4I_TCON_GCTL_REG,
 			   SUN4I_TCON_GCTL_IOMAP_MASK,
@@ -1500,6 +1524,7 @@ static const struct sun4i_tcon_quirks sun8i_a83t_tv_quirks = {
 
 static const struct sun4i_tcon_quirks sun8i_r40_tv_quirks = {
 	.has_channel_1		= true,
+	.polarity_in_ch0	= true,
 	.set_mux		= sun8i_r40_tcon_tv_set_mux,
 };
 
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index c5ac1b02482c..e624f6977eb8 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -154,6 +154,11 @@
 #define SUN4I_TCON1_BASIC5_V_SYNC(height)		(((height) - 1) & 0x3ff)
 
 #define SUN4I_TCON1_IO_POL_REG			0xf0
+/* there is no documentation about this bit */
+#define SUN4I_TCON1_IO_POL_UNKNOWN			BIT(26)
+#define SUN4I_TCON1_IO_POL_HSYNC_POSITIVE		BIT(25)
+#define SUN4I_TCON1_IO_POL_VSYNC_POSITIVE		BIT(24)
+
 #define SUN4I_TCON1_IO_TRI_REG			0xf4
 
 #define SUN4I_TCON_ECC_FIFO_REG			0xf8
@@ -236,6 +241,7 @@ 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? */
+	bool	polarity_in_ch0; /* some tcon1 channels have polarity bits in tcon0 pol register */
 	u8	dclk_min_div;	/* minimum divider for TCON0 DCLK */
 
 	/* callback to handle tcon muxing options */
-- 
2.30.0