[PATCH 3/3] drm/bridge: ti-sn65dsi83: add test pattern generation support

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Generation of a test pattern output is a useful tool for panel bringup and
debugging, and very simple to support with this chip.

The value of REG_VID_CHA_ACTIVE_LINE_LENGTH_LOW needs to be divided by two
for the test pattern to work in dual LVDS mode. While not clearly stated in
the datasheet, this is needed according to the DSI Tuner [0] output. And
some dual-LVDS panels refuse to show any picture without this division by
two.

[0] https://www.ti.com/tool/DSI-TUNER

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 17a885244e1e..ddc8b5e1dd15 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -114,6 +114,7 @@
 #define REG_VID_CHA_HORIZONTAL_FRONT_PORCH	0x38
 #define REG_VID_CHA_VERTICAL_FRONT_PORCH	0x3a
 #define REG_VID_CHA_TEST_PATTERN		0x3c
+#define  REG_VID_CHA_TEST_PATTERN_EN		BIT(4)
 /* IRQ registers */
 #define REG_IRQ_GLOBAL				0xe0
 #define  REG_IRQ_GLOBAL_IRQ_EN			BIT(0)
@@ -134,6 +135,9 @@
 #define  REG_IRQ_STAT_CHA_SOT_BIT_ERR		BIT(2)
 #define  REG_IRQ_STAT_CHA_PLL_UNLOCK		BIT(0)
 
+static bool sn65dsi83_test_pattern;
+module_param_named(test_pattern, sn65dsi83_test_pattern, bool, 0644);
+
 enum sn65dsi83_channel {
 	CHANNEL_A,
 	CHANNEL_B
@@ -645,7 +649,11 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 			  REG_LVDS_LANE_CHB_LVDS_TERM : 0));
 	regmap_write(ctx->regmap, REG_LVDS_CM, 0x00);
 
-	le16val = cpu_to_le16(mode->hdisplay);
+	/*
+	 * Active line length needs to be halved for test pattern
+	 * generation in dual LVDS output.
+	 */
+	le16val = cpu_to_le16(mode->hdisplay / (sn65dsi83_test_pattern ? 2 : 1));
 	regmap_bulk_write(ctx->regmap, REG_VID_CHA_ACTIVE_LINE_LENGTH_LOW,
 			  &le16val, 2);
 	le16val = cpu_to_le16(mode->vdisplay);
@@ -668,7 +676,8 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 		     (mode->hsync_start - mode->hdisplay) / dual_factor);
 	regmap_write(ctx->regmap, REG_VID_CHA_VERTICAL_FRONT_PORCH,
 		     mode->vsync_start - mode->vdisplay);
-	regmap_write(ctx->regmap, REG_VID_CHA_TEST_PATTERN, 0x00);
+	regmap_write(ctx->regmap, REG_VID_CHA_TEST_PATTERN,
+		     sn65dsi83_test_pattern ? REG_VID_CHA_TEST_PATTERN_EN : 0);
 
 	/* Enable PLL */
 	regmap_write(ctx->regmap, REG_RC_PLL_EN, REG_RC_PLL_EN_PLL_EN);

-- 
2.53.0