drm/bridge: ti-sn65dsi83: add test pattern generation support

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

Reviewed-by: Louis Chauvet <louis.chauvet@boootlin.com>
Link: https://patch.msgid.link/20260416-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v3-1-143886aebc6b@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 17a8852..2b6f6a5 100644 (file)
--- 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
@@ -523,6 +527,7 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
        const struct drm_display_mode *mode;
        struct drm_connector *connector;
        struct drm_crtc *crtc;
+       bool test_pattern = sn65dsi83_test_pattern;
        bool lvds_format_24bpp;
        bool lvds_format_jeida;
        unsigned int pval;
@@ -645,7 +650,11 @@ 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 / (test_pattern ? dual_factor : 1));
        regmap_bulk_write(ctx->regmap, REG_VID_CHA_ACTIVE_LINE_LENGTH_LOW,
                          &le16val, 2);
        le16val = cpu_to_le16(mode->vdisplay);
@@ -668,7 +677,8 @@ 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,
+                    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);