[PATCH] drm/bridge: tc358768: Enforce input bus flags via atomic_check

[Leonardo Costa <leoreis.costa@gmail.com>]

From: Leonardo Costa <leonardo.costa@toradex.com>

The tc358768 declares static bridge timings requiring pixel data to be
sampled on the positive clock edge.

However, the DRM core default propagation simply copies the output-side
bus flags, coming from the next bridge, connector or panel, to the
input side. If the propagated flags are incompatible with the bridge
ones, the data is wrongly sampled, typically resulting in visual
artifacts on the panel.

Implement the atomic_check hook, replacing the mutually exclusive
mode_fixup, and set the bridge state input bus flags to the ones
required by the tc358768. The sync polarity defaulting previously done
in mode_fixup is carried over into atomic_check unchanged.

Fixes: ff1ca6397b1d ("drm/bridge: Add tc358768 driver")
Cc: stable@vger.kernel.org
Signed-off-by: Leonardo Costa <leonardo.costa@toradex.com>
---
 drivers/gpu/drm/bridge/tc358768.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358768.c b/drivers/gpu/drm/bridge/tc358768.c
index 0d85120fcc7a3..0516a331e71ba 100644
--- a/drivers/gpu/drm/bridge/tc358768.c
+++ b/drivers/gpu/drm/bridge/tc358768.c
@@ -1262,10 +1262,13 @@ tc358768_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
 	return input_fmts;
 }
 
-static bool tc358768_mode_fixup(struct drm_bridge *bridge,
-				const struct drm_display_mode *mode,
-				struct drm_display_mode *adjusted_mode)
+static int tc358768_bridge_atomic_check(struct drm_bridge *bridge,
+					struct drm_bridge_state *bridge_state,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state)
 {
+	struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
+
 	/* Default to positive sync */
 
 	if (!(adjusted_mode->flags &
@@ -1276,13 +1279,15 @@ static bool tc358768_mode_fixup(struct drm_bridge *bridge,
 	      (DRM_MODE_FLAG_PVSYNC | DRM_MODE_FLAG_NVSYNC)))
 		adjusted_mode->flags |= DRM_MODE_FLAG_PVSYNC;
 
-	return true;
+	bridge_state->input_bus_cfg.flags = bridge->timings->input_bus_flags;
+
+	return 0;
 }
 
 static const struct drm_bridge_funcs tc358768_bridge_funcs = {
 	.attach = tc358768_bridge_attach,
 	.mode_valid = tc358768_bridge_mode_valid,
-	.mode_fixup = tc358768_mode_fixup,
+	.atomic_check = tc358768_bridge_atomic_check,
 	.atomic_pre_enable = tc358768_bridge_atomic_pre_enable,
 	.atomic_enable = tc358768_bridge_atomic_enable,
 	.atomic_disable = tc358768_bridge_atomic_disable,