[PATCH v4 5/7] drm/sun4i: tcon: Support the LVDS Dual-Link

[Maxime Ripard <maxime@cerno.tech>]

The A20 and other SoC with two TCONs (A31, R40, etc.) can use its second
TCON as the secondary LVDS link in a dual-link setup, with the TCON0 being
the main link. Extend a bit the parsing code to leverage the DRM dual-link
code, register only the LVDS output on the primary TCON, and add the needed
bits to setup the TCON properly.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/sun4i/sun4i_tcon.c | 36 ++++++++++++++++++++++++++++++
 drivers/gpu/drm/sun4i/sun4i_tcon.h |  4 ++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.c b/drivers/gpu/drm/sun4i/sun4i_tcon.c
index 32757175f86b..005c37831eb6 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.c
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.c
@@ -475,6 +475,10 @@ static void sun4i_tcon0_mode_set_lvds(struct sun4i_tcon *tcon,
 		     SUN4I_TCON0_BASIC2_V_BACKPORCH(bp));
 
 	reg = SUN4I_TCON0_LVDS_IF_CLK_SEL_TCON0;
+
+	if (tcon->lvds_dual_link)
+		reg |= SUN4I_TCON0_LVDS_IF_DUAL_LINK;
+
 	if (sun4i_tcon_get_pixel_depth(encoder) == 24)
 		reg |= SUN4I_TCON0_LVDS_IF_BITWIDTH_24BITS;
 	else
@@ -903,6 +907,16 @@ static int sun4i_tcon_register_panel(struct drm_device *drm,
 	    !of_device_is_compatible(remote, "panel-lvds"))
 		return sun4i_rgb_init(drm, tcon);
 
+	/*
+	 * Only the TCON0 will be relevant for the LVDS output, so if
+	 * our ID is something else, let's prevent our TCON from
+	 * registering its own LVDS output
+	 */
+	if (tcon->id) {
+		dev_dbg(dev, "TCON used as an LVDS secondary link.");
+		return 0;
+	}
+
 	/*
 	 * This can only be made optional since we've had DT
 	 * nodes without the LVDS reset properties.
@@ -939,6 +953,28 @@ static int sun4i_tcon_register_panel(struct drm_device *drm,
 		}
 	}
 
+	/*
+	 * If we don't have a second TCON, we will never be able to do
+	 * dual-link LVDS, so we don't have much more to do.
+	 */
+	companion = of_parse_phandle(dev->of_node, "link-companion", 0);
+	if (!companion)
+		return sun4i_lvds_init(drm, tcon);
+
+	/*
+	 * Let's do a sanity check on the dual-link setup to make sure
+	 * everything is properly described.
+	 */
+	ret = drm_of_lvds_get_dual_link_pixel_order(dev->of_node, 1, 0,
+						    companion, 1, 0);
+	if (ret < 0) {
+		dev_err(dev, "Invalid Dual-Link Configuration.\n");
+		return ret;
+	}
+
+	dev_info(dev, "Primary TCON, enabling LVDS Dual-Link");
+	tcon->lvds_dual_link = true;
+
 	return sun4i_lvds_init(drm, tcon);
 }
 
diff --git a/drivers/gpu/drm/sun4i/sun4i_tcon.h b/drivers/gpu/drm/sun4i/sun4i_tcon.h
index ee555318e3c2..f6a589828f94 100644
--- a/drivers/gpu/drm/sun4i/sun4i_tcon.h
+++ b/drivers/gpu/drm/sun4i/sun4i_tcon.h
@@ -98,6 +98,7 @@
 
 #define SUN4I_TCON0_LVDS_IF_REG			0x84
 #define SUN4I_TCON0_LVDS_IF_EN				BIT(31)
+#define SUN4I_TCON0_LVDS_IF_DUAL_LINK			BIT(30)
 #define SUN4I_TCON0_LVDS_IF_BITWIDTH_MASK		BIT(26)
 #define SUN4I_TCON0_LVDS_IF_BITWIDTH_18BITS		(1 << 26)
 #define SUN4I_TCON0_LVDS_IF_BITWIDTH_24BITS		(0 << 26)
@@ -280,6 +281,9 @@ struct sun4i_tcon {
 	/* Associated crtc */
 	struct sun4i_crtc		*crtc;
 
+	/* Is the LVDS link a dual-channel link? */
+	bool				lvds_dual_link;
+
 	int				id;
 
 	/* TCON list management */
-- 
2.29.2


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