drm/tegra: rgb: Parameterize V- and H-sync polarities

The polarities of the V- and H-sync signals are encoded as flags in the
display mode, so use the existing information to setup the signals for
the RGB interface.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
[tomi.valkeinen@ideasonboard.com: default to positive sync]
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906-tc358768-v4-1-31725f008a50@ideasonboard.com

drivers/gpu/drm/tegra/rgb.c

@@ -99,6 +99,7 @@ static void tegra_rgb_encoder_disable(struct drm_encoder *encoder)
 
 static void tegra_rgb_encoder_enable(struct drm_encoder *encoder)
 {
+	struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
 	struct tegra_output *output = encoder_to_output(encoder);
 	struct tegra_rgb *rgb = to_rgb(output);
 	u32 value;
@@ -108,10 +109,19 @@ static void tegra_rgb_encoder_enable(struct drm_encoder *encoder)
 	value = DE_SELECT_ACTIVE | DE_CONTROL_NORMAL;
 	tegra_dc_writel(rgb->dc, value, DC_DISP_DATA_ENABLE_OPTIONS);
 
-	/* XXX: parameterize? */
+	/* configure H- and V-sync signal polarities */
 	value = tegra_dc_readl(rgb->dc, DC_COM_PIN_OUTPUT_POLARITY(1));
-	value &= ~LVS_OUTPUT_POLARITY_LOW;
+
+	if (mode->flags & DRM_MODE_FLAG_NHSYNC)
+		value |= LHS_OUTPUT_POLARITY_LOW;
+	else
 		value &= ~LHS_OUTPUT_POLARITY_LOW;
+
+	if (mode->flags & DRM_MODE_FLAG_NVSYNC)
+		value |= LVS_OUTPUT_POLARITY_LOW;
+	else
+		value &= ~LVS_OUTPUT_POLARITY_LOW;
+
 	tegra_dc_writel(rgb->dc, value, DC_COM_PIN_OUTPUT_POLARITY(1));
 
 	/* XXX: parameterize? */