[PATCH v5 1/2] drm: Add detection of changing of edid on between suspend and resume

[Gwan-gyeong Mun]

The hotplug detection routine of drm_helper_hpd_irq_event() can detect
changing of status of connector, but it can not detect changing of edid.

Following scenario requires detection of changing of edid.

 1) plug display device to a connector
 2) system suspend
 3) unplug 1)'s display device and plug the other display device to a
    connector
 4) system resume

It adds edid check routine when a connector status still remains as
"connector_status_connected".

v2: Add NULL check before comparing of EDIDs.
v3: Make it as part of existing drm_helper_hpd_irq_event() (Stan, Mika)
v4: Rebased
v5: Use a cached edid property blob data of connector instead of adding
    a new detected_edid variable. (Maarten)
    Add an using of reference count for getting a cached edid property
    blob data. (Maarten)

Testcase: igt/kms_chamelium/hdmi-edid-change-during-hibernate
Testcase: igt/kms_chamelium/hdmi-edid-change-during-suspend
Testcase: igt/kms_chamelium/dp-edid-change-during-hibernate
Testcase: igt/kms_chamelium/dp-edid-change-during-suspend

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
---
 drivers/gpu/drm/drm_probe_helper.c | 34 +++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 6fd08e04b323..27ad7f3dabb7 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -742,7 +742,16 @@ EXPORT_SYMBOL(drm_kms_helper_poll_fini);
  * panels.
  *
  * This helper function is useful for drivers which can't or don't track hotplug
- * interrupts for each connector.
+ * interrupts for each connector. And it also supports a detection of changing
+ * of edid on between suspend and resume when a connector status still remains
+ * as "connector_status_connected".
+ *
+ * Following scenario requires detection of changing of edid.
+ *  1) plug display device to a connector
+ *  2) system suspend
+ *  3) unplug 1)'s display device and plug the other display device to a
+ *     connector
+ *  4) system resume
  *
  * Drivers which support hotplug interrupts for each connector individually and
  * which have a more fine-grained detect logic should bypass this code and
@@ -760,6 +769,7 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 	struct drm_connector *connector;
 	struct drm_connector_list_iter conn_iter;
 	enum drm_connector_status old_status;
+	struct drm_property_blob *old_edid_blob_ptr;
 	bool changed = false;
 
 	if (!dev->mode_config.poll_enabled)
@@ -774,6 +784,11 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 
 		old_status = connector->status;
 
+		if (connector->edid_blob_ptr)
+			old_edid_blob_ptr = drm_property_blob_get(connector->edid_blob_ptr);
+		else
+			old_edid_blob_ptr = NULL;
+
 		connector->status = drm_helper_probe_detect(connector, NULL, false);
 		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] status updated from %s to %s\n",
 			      connector->base.id,
@@ -782,6 +797,23 @@ bool drm_helper_hpd_irq_event(struct drm_device *dev)
 			      drm_get_connector_status_name(connector->status));
 		if (old_status != connector->status)
 			changed = true;
+
+		/* Check changing of edid when a connector status still remains
+		 * as "connector_status_connected".
+		 */
+		if (old_edid_blob_ptr && connector->edid_blob_ptr &&
+		    old_status == connector->status &&
+		    old_status == connector_status_connected) {
+			if (memcmp(old_edid_blob_ptr->data,
+				connector->edid_blob_ptr->data,
+				old_edid_blob_ptr->length)) {
+				changed = true;
+				DRM_DEBUG_KMS("[CONNECTOR:%d:%s] edid updated\n",
+					      connector->base.id,
+					      connector->name);
+			}
+		}
+		drm_property_blob_put(old_edid_blob_ptr);
 	}
 	drm_connector_list_iter_end(&conn_iter);
 	mutex_unlock(&dev->mode_config.mutex);
-- 
2.21.0