drm/bridge: Add helper to reset bridge pipeline

Let's provide an helper to make it easier for bridge drivers to
power-cycle their bridge.

In order to avoid a circular dependency between that new helper and
drm_atomic_helper_reset_crtc(), this new helper will be in a
drm_bridge_helper.c file to follow the pattern we have for other
objects.

Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Tested-by: Herve Codina <herve.codina@bootlin.com>
Co-developed-by: Simona Vetter <simona.vetter@intel.com>
Signed-off-by: Simona Vetter <simona.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250313-bridge-connector-v6-8-511c54a604fb@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

drivers/gpu/drm/Makefile

@@ -133,6 +133,7 @@ obj-$(CONFIG_DRM_TTM_HELPER) += drm_ttm_helper.o
 drm_kms_helper-y := \
 	drm_atomic_helper.o \
 	drm_atomic_state_helper.o \
+	drm_bridge_helper.o \
 	drm_crtc_helper.o \
 	drm_damage_helper.o \
 	drm_flip_work.o \

drivers/gpu/drm/drm_atomic_helper.c

@@ -3409,6 +3409,9 @@ EXPORT_SYMBOL(drm_atomic_helper_disable_all);
  * This implies a reset of all active components available between the CRTC and
  * connectors.
  *
+ * A variant of this function exists with
+ * drm_bridge_helper_reset_crtc(), dedicated to bridges.
+ *
  * NOTE: This relies on resetting &drm_crtc_state.connectors_changed.
  * For drivers which optimize out unnecessary modesets this will result in
  * a no-op commit, achieving nothing.

drivers/gpu/drm/drm_bridge_helper.c

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <drm/drm_atomic.h>
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_bridge.h>
+#include <drm/drm_bridge_helper.h>
+#include <drm/drm_modeset_lock.h>
+
+/**
+ * drm_bridge_helper_reset_crtc - Reset the pipeline feeding a bridge
+ * @bridge: DRM bridge to reset
+ * @ctx: lock acquisition context
+ *
+ * Reset a @bridge pipeline. It will power-cycle all active components
+ * between the CRTC and connector that bridge is connected to.
+ *
+ * As it relies on drm_atomic_helper_reset_crtc(), the same limitations
+ * apply.
+ *
+ * Returns:
+ *
+ * 0 on success or a negative error code on failure. If the error
+ * returned is EDEADLK, the whole atomic sequence must be restarted.
+ */
+int drm_bridge_helper_reset_crtc(struct drm_bridge *bridge,
+				 struct drm_modeset_acquire_ctx *ctx)
+{
+	struct drm_connector *connector;
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_device *dev = encoder->dev;
+	struct drm_crtc *crtc;
+	int ret;
+
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
+	if (ret)
+		return ret;
+
+	connector = drm_atomic_get_connector_for_encoder(encoder, ctx);
+	if (IS_ERR(connector)) {
+		ret = PTR_ERR(connector);
+		goto out;
+	}
+
+	if (!connector->state) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	crtc = connector->state->crtc;
+	ret = drm_atomic_helper_reset_crtc(crtc, ctx);
+	if (ret)
+		goto out;
+
+out:
+	drm_modeset_unlock(&dev->mode_config.connection_mutex);
+	return ret;
+}
+EXPORT_SYMBOL(drm_bridge_helper_reset_crtc);

include/drm/drm_bridge_helper.h

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __DRM_BRIDGE_HELPER_H_
+#define __DRM_BRIDGE_HELPER_H_
+
+struct drm_bridge;
+struct drm_modeset_acquire_ctx;
+
+int drm_bridge_helper_reset_crtc(struct drm_bridge *bridge,
+				 struct drm_modeset_acquire_ctx *ctx);
+
+#endif // __DRM_BRIDGE_HELPER_H_