The drm_display_mode_to_videomode() does not populate DISPLAY_FLAGS_DE_LOW
or DISPLAY_FLAGS_PIXDATA_NEGEDGE flags in struct videomode. Therefore, no
matter what polarity the next bridge or display might require, these flags
are never set, and thus the LTDC GCR_DEPOL and GCR_PCPOL bits are never set,
and the LTDC behaves as if both DISPLAY_FLAGS_PIXDATA_POSEDGE and
DISPLAY_FLAGS_DE_HIGH were always set.

The fix for this problem is taken almost verbatim from MXSFB driver. In
case there is a bridge attached to the LTDC, the bridge might have extra
polarity requirements, so extract bus_flags from the bridge and use them
for LTDC configuration. Otherwise, extract bus_flags from the connector,
which is the display.

Fixes: b759012c5fa7 ("drm/stm: Add STM32 LTDC driver")
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Yannick Fertre <redacted>
Cc: Alexandre Torgue <redacted>
Cc: Antonio Borneo <redacted>
Cc: Benjamin Gaignard <redacted>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Philippe Cornu <redacted>
Cc: Sam Ravnborg <redacted>
Cc: Vincent Abriou <redacted>
Cc: Yannick Fertre <redacted>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-stm32@st-md-mailman.stormreply.com
To: dri-devel@lists.freedesktop.org
---
V2: Check if ldev->bridge->timings is non-NULL before accessing it
V3: get bus_flags from connector (from Yannick)
     - Display controller could support several connectors (not connected at
       the same time). ie: stm32mp15c-DK2 board have 2 connectors (HDMI + DSI).
       Driver check which connector is connected to get the bus flag.
V4: get bridge from encoder (from Yannick)
---
  drivers/gpu/drm/stm/ltdc.c | 33 +++++++++++++++++++++++++++++++--
  1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 6e28e6b60e72..acc9f6694eb6 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c

@@ -544,13 +544,42 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
  {
  	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
  	struct drm_device *ddev = crtc->dev;
+	struct drm_connector_list_iter iter;
+	struct drm_connector *connector = NULL;
+	struct drm_encoder *encoder = NULL;
+	struct drm_bridge *bridge = NULL;
  	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
  	struct videomode vm;
  	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
  	u32 total_width, total_height;
+	u32 bus_flags = 0;
  	u32 val;
  	int ret;
  
+	/* get encoder from crtc */
+	drm_for_each_encoder(encoder, ddev)
+		if (encoder->crtc == crtc)
+			break;
+
+	if (encoder) {
+		/* get bridge from encoder */
+		list_for_each_entry(bridge, &encoder->bridge_chain, chain_node)
+			if (bridge->encoder == encoder)
+				break;
+
+		/* Get the connector from encoder */
+		drm_connector_list_iter_begin(ddev, &iter);
+		drm_for_each_connector_iter(connector, &iter)
+			if (connector->encoder == encoder)
+				break;
+		drm_connector_list_iter_end(&iter);
+	}
+
+	if (bridge && bridge->timings)
+		bus_flags = bridge->timings->input_bus_flags;
+	else if (connector)
+		bus_flags = connector->display_info.bus_flags;
+
  	if (!pm_runtime_active(ddev->dev)) {
  		ret = pm_runtime_get_sync(ddev->dev);
  		if (ret) {

@@ -586,10 +615,10 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
  	if (vm.flags & DISPLAY_FLAGS_VSYNC_HIGH)
  		val |= GCR_VSPOL;
  
-	if (vm.flags & DISPLAY_FLAGS_DE_LOW)
+	if (bus_flags & DRM_BUS_FLAG_DE_LOW)
  		val |= GCR_DEPOL;
  
-	if (vm.flags & DISPLAY_FLAGS_PIXDATA_NEGEDGE)
+	if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
  		val |= GCR_PCPOL;
  
  	reg_update_bits(ldev->regs, LTDC_GCR,