[PATCH V2] drm/stm: Fix bus_flags handling

Marek Vasut marex at denx.de
Thu Dec 24 01:19:53 EST 2020

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 at denx.de>
Cc: Alexandre Torgue <alexandre.torgue at st.com>
Cc: Antonio Borneo <antonio.borneo at st.com>
Cc: Benjamin Gaignard <benjamin.gaignard at st.com>
Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
Cc: Philippe Cornu <philippe.cornu at st.com>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: Vincent Abriou <vincent.abriou at st.com>
Cc: Yannick Fertre <yannick.fertre at st.com>
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-stm32 at st-md-mailman.stormreply.com
To: dri-devel at lists.freedesktop.org
V2: Check if ldev->bridge->timings is non-NULL before accessing it
 drivers/gpu/drm/stm/ltdc.c | 22 ++++++++++++++++++++--
 drivers/gpu/drm/stm/ltdc.h |  2 ++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 1c9f18b4adfc..22c7e9fa5ab7 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -546,11 +546,17 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	struct drm_device *ddev = crtc->dev;
 	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
 	struct videomode vm;
+	u32 bus_flags = 0;
 	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
 	u32 total_width, total_height;
 	u32 val;
 	int ret;
+	if (ldev->bridge && ldev->bridge->timings)
+		bus_flags = ldev->bridge->timings->input_bus_flags;
+	else if (ldev->connector)
+		bus_flags = ldev->connector->display_info.bus_flags;
 	if (!pm_runtime_active(ddev->dev)) {
 		ret = pm_runtime_get_sync(ddev->dev);
 		if (ret) {
@@ -586,10 +592,10 @@ 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;
 		val |= GCR_PCPOL;
 	reg_update_bits(ldev->regs, LTDC_GCR,
@@ -1098,6 +1104,8 @@ static const struct drm_encoder_helper_funcs ltdc_encoder_helper_funcs = {
 static int ltdc_encoder_init(struct drm_device *ddev, struct drm_bridge *bridge)
+	struct ltdc_device *ldev = ddev->dev_private;
+	struct drm_connector_list_iter iter;
 	struct drm_encoder *encoder;
 	int ret;
@@ -1119,6 +1127,16 @@ static int ltdc_encoder_init(struct drm_device *ddev, struct drm_bridge *bridge)
 		return -EINVAL;
+	ldev->bridge = bridge;
+	/*
+	 * Get hold of the connector. This is a bit of a hack, until the bridge
+	 * API gives us bus flags and formats.
+	 */
+	drm_connector_list_iter_begin(ddev, &iter);
+	ldev->connector = drm_connector_list_iter_next(&iter);
+	drm_connector_list_iter_end(&iter);
 	DRM_DEBUG_DRIVER("Bridge encoder:%d created\n", encoder->base.id);
 	return 0;
diff --git a/drivers/gpu/drm/stm/ltdc.h b/drivers/gpu/drm/stm/ltdc.h
index f153b908c70e..d0d2c81de29a 100644
--- a/drivers/gpu/drm/stm/ltdc.h
+++ b/drivers/gpu/drm/stm/ltdc.h
@@ -38,6 +38,8 @@ struct ltdc_device {
 	u32 irq_status;
 	struct fps_info plane_fpsi[LTDC_MAX_LAYER];
 	struct drm_atomic_state *suspend_state;
+	struct drm_bridge *bridge;
+	struct drm_connector *connector;
 int ltdc_load(struct drm_device *ddev);

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