From 3682d604ecbdd233bb7e38b8e18f0496d78a8969 Mon Sep 17 00:00:00 2001
From: Yannick Fertre <yannick.fertre@foss.st.com>
Date: Thu, 31 Oct 2024 08:56:07 +0100
Subject: [PATCH] drm/stm: ltdc: reset ltdc on crtc enable

To avoid any blocking point between uboot and the kernel,
ltdc must be reset. To have a continuous display,
the reset is conditional on the boolean "default-on".
The reset must be done when activating the crtc.

Change-Id: I1f8c31087ea28fab4ff56400f1aa863541ed08c3
Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/416185
---
 drivers/gpu/drm/stm/ltdc.c | 21 +++++++++++++++------
 drivers/gpu/drm/stm/ltdc.h |  1 +
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 2a25119cd9959a..11fb670c600c01 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -810,8 +810,18 @@ static void ltdc_crtc_atomic_enable(struct drm_crtc *crtc,
 
 	DRM_DEBUG_DRIVER("\n");
 
-	if (pm_runtime_active(ddev->dev))
+	if (pm_runtime_active(ddev->dev)) {
+		if (!IS_ERR(ldev->rstc)) {
+			reset_control_assert(ldev->rstc);
+			usleep_range(10, 20);
+			reset_control_deassert(ldev->rstc);
+		}
+
+		/* Wait a while to clear the current display */
+		mdelay(30);
+
 		pm_runtime_put_sync_suspend(ddev->dev);
+	}
 
 	/* get encoder from crtc */
 	drm_for_each_encoder(en_iter, ddev)
@@ -2413,7 +2423,6 @@ int ltdc_load(struct drm_device *ddev)
 	struct drm_bridge *bridge;
 	struct drm_panel *panel;
 	struct drm_crtc *crtc;
-	struct reset_control *rstc;
 	struct resource *res;
 	int irq, i, nb_endpoints;
 	int ret = -ENODEV;
@@ -2472,7 +2481,7 @@ int ltdc_load(struct drm_device *ddev)
 		}
 	}
 
-	rstc = devm_reset_control_get_exclusive(dev, NULL);
+	ldev->rstc = devm_reset_control_get_exclusive(dev, NULL);
 
 	mutex_init(&ldev->err_lock);
 
@@ -2483,10 +2492,10 @@ int ltdc_load(struct drm_device *ddev)
 	 * remain activated and reset shouldn't be done
 	 */
 	if (!def_value) {
-		if (!IS_ERR(rstc)) {
-			reset_control_assert(rstc);
+		if (!IS_ERR(ldev->rstc)) {
+			reset_control_assert(ldev->rstc);
 			usleep_range(10, 20);
-			reset_control_deassert(rstc);
+			reset_control_deassert(ldev->rstc);
 		}
 	}
 
diff --git a/drivers/gpu/drm/stm/ltdc.h b/drivers/gpu/drm/stm/ltdc.h
index 8d58bc93a460b6..356033af6b9b7f 100644
--- a/drivers/gpu/drm/stm/ltdc.h
+++ b/drivers/gpu/drm/stm/ltdc.h
@@ -71,6 +71,7 @@ struct ltdc_device {
 	u32 crc;
 	u32 max_burst_length;
 	struct reserved_mem *rot_mem;
+	struct reset_control *rstc;
 	struct stm32_firewall firewall[LTDC_MAX_FIREWALL];
 	bool plane_enabled[LTDC_MAX_LAYER];
 };