drm/ast: Implement polling for VGA and SIL164 connectors

Implement polling for VGA and SIL164 connectors. Set the flag
DRM_CONNECTOR_POLL_DISCONNECT for each to detect the removal of the
monitor cable. Implement struct drm_connector_helper_funcs.detect_ctx
for each type of connector by testing for EDID data.

The helper drm_connector_helper_detect_ctx() implements .detect_ctx()
on top of the connector's DDC channel. The function can be used by
other drivers as companion to drm_connector_helper_get_modes().

v6:
- change helper name to drm_connector_helper_detec_from_ddc()
  (Maxime, Sui)
v5:
- share implementation in drm_connector_helper_detect_ctx() (Maxime)
- test for DDC presence with drm_probe_ddc() (Maxime, Jani)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Acked-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-13-tzimmermann@suse.de

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index bf2dd1f46b6c..8fb842c6c638 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -1279,3 +1279,32 @@ int drm_connector_helper_tv_get_modes(struct drm_connector *connector)
 	return i;
 }
 EXPORT_SYMBOL(drm_connector_helper_tv_get_modes);
+
+/**
+ * drm_connector_helper_detect_from_ddc - Read EDID and detect connector status.
+ * @connector: The connector
+ * @ctx: Acquire context
+ * @force: Perform screen-destructive operations, if necessary
+ *
+ * Detects the connector status by reading the EDID using drm_probe_ddc(),
+ * which requires connector->ddc to be set. Returns connector_status_connected
+ * on success or connector_status_disconnected on failure.
+ *
+ * Returns:
+ * The connector status as defined by enum drm_connector_status.
+ */
+int drm_connector_helper_detect_from_ddc(struct drm_connector *connector,
+					 struct drm_modeset_acquire_ctx *ctx,
+					 bool force)
+{
+	struct i2c_adapter *ddc = connector->ddc;
+
+	if (!ddc)
+		return connector_status_unknown;
+
+	if (drm_probe_ddc(ddc))
+		return connector_status_connected;
+
+	return connector_status_disconnected;
+}
+EXPORT_SYMBOL(drm_connector_helper_detect_from_ddc);