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Subject[PATCH v2 2/5] drm/sun4i: tcon: set sync polarity for tcon1 channel
Date
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@csie.org>
Tested-by: Andre Heider <a.heider@gmail.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@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
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