From eb3ff3f44ac4daf06279c6e566e4fcb99ff1988d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonas=20=C3=85dahl?= <jadahl@gmail.com>
Date: Fri, 10 Mar 2017 16:55:53 +0800
Subject: [PATCH] monitor-manager-kms: Don't try to wait for EDID on hot plug

The mitigation to avoid missing EDID blob was incorrect; the reason it
sometimes failed to read was a race between different applications all
trying to read the EDID at the same time. E.g. gnome-shell as GDM would
at the same time as the session gnome-shell try to read the EDID of the
same connector at the same time, triggering a race in the kernel,
making the blob reading ioctl occationally fail with ENOENT.

Remove this mitigation, as it didn't really mitigate anything; the race
could just as well happen when doing the actual read later.

https://bugzilla.gnome.org/show_bug.cgi?id=779837
---
 .../native/meta-monitor-manager-kms.c         | 130 ------------------
 1 file changed, 130 deletions(-)

diff --git a/src/backends/native/meta-monitor-manager-kms.c b/src/backends/native/meta-monitor-manager-kms.c
index 5256b4775..202567600 100644
--- a/src/backends/native/meta-monitor-manager-kms.c
+++ b/src/backends/native/meta-monitor-manager-kms.c
@@ -52,10 +52,6 @@
 #define ALL_TRANSFORMS_MASK ((1 << ALL_TRANSFORMS) - 1)
 #define SYNC_TOLERANCE 0.01    /* 1 percent */
 
-/* Try each 50 milleseconds up to half a second to get a proper EDID read */
-#define EDID_RETRY_TIMEOUT_MS 50
-#define EDID_MAX_NUM_RETRIES 10
-
 typedef struct
 {
   drmModeConnector *connector;
@@ -117,9 +113,6 @@ struct _MetaMonitorManagerKms
   GSettings *desktop_settings;
 
   gboolean page_flips_not_supported;
-
-  guint handle_hotplug_timeout;
-  int read_edid_tries;
 };
 
 struct _MetaMonitorManagerKmsClass
@@ -1595,76 +1588,6 @@ meta_monitor_manager_kms_set_crtc_gamma (MetaMonitorManager *manager,
   drmModeCrtcSetGamma (manager_kms->fd, crtc->crtc_id, size, red, green, blue);
 }
 
-static gboolean
-has_pending_edid_blob (MetaMonitorManagerKms *manager_kms)
-{
-  drmModeRes *resources;
-  int n_connectors;
-  int i, j;
-  gboolean edid_blob_pending;
-
-  resources = drmModeGetResources (manager_kms->fd);
-  n_connectors = resources->count_connectors;
-
-  edid_blob_pending = FALSE;
-  for (i = 0; i < n_connectors; i++)
-    {
-      drmModeConnector *drm_connector;
-      uint32_t edid_blob_id;
-
-      drm_connector = drmModeGetConnector (manager_kms->fd,
-                                           resources->connectors[i]);
-
-      edid_blob_id = 0;
-      for (j = 0; j < drm_connector->count_props; j++)
-        {
-          drmModePropertyPtr prop;
-
-          prop = drmModeGetProperty (manager_kms->fd, drm_connector->props[j]);
-
-          if (prop->flags & DRM_MODE_PROP_BLOB &&
-              g_str_equal (prop->name, "EDID"))
-            edid_blob_id = drm_connector->prop_values[j];
-
-          drmModeFreeProperty (prop);
-
-          if (edid_blob_id)
-            break;
-        }
-
-      drmModeFreeConnector (drm_connector);
-
-      if (edid_blob_id)
-        {
-          GError *error = NULL;
-          drmModePropertyBlobPtr edid_blob;
-
-          edid_blob = read_edid_blob (manager_kms, edid_blob_id, &error);
-          if (!edid_blob &&
-              g_error_matches (error, G_IO_ERROR, G_IO_ERROR_NOT_FOUND))
-            {
-              edid_blob_pending = TRUE;
-              g_error_free (error);
-            }
-          else if (!edid_blob)
-            {
-              g_error_free (error);
-            }
-          else
-            {
-              drmModeFreePropertyBlob (edid_blob);
-            }
-        }
-
-      if (edid_blob_pending)
-        break;
-    }
-
-  drmModeFreeResources (resources);
-
-  return edid_blob_pending;
-}
-
 static void
 handle_hotplug_event (MetaMonitorManager *manager)
 {
@@ -1672,37 +1595,6 @@ handle_hotplug_event (MetaMonitorManager *manager)
   meta_monitor_manager_on_hotplug (manager);
 }
 
-static gboolean
-handle_hotplug_event_timeout (gpointer user_data)
-{
-  MetaMonitorManager *manager = user_data;
-  MetaMonitorManagerKms *manager_kms = META_MONITOR_MANAGER_KMS (user_data);
-
-  if (!has_pending_edid_blob (manager_kms))
-    {
-      handle_hotplug_event (manager);
-
-      manager_kms->handle_hotplug_timeout = 0;
-      return G_SOURCE_REMOVE;
-    }
-
-  manager_kms->read_edid_tries++;
-
-  if (manager_kms->read_edid_tries > EDID_MAX_NUM_RETRIES)
-    {
-      g_warning ("Tried to read the EDID %d times, "
-                 "but one or more are still missing, continuing without",
-                 manager_kms->read_edid_tries);
-
-      handle_hotplug_event (manager);
-
-      manager_kms->handle_hotplug_timeout = 0;
-      return G_SOURCE_REMOVE;
-    }
-
-  return G_SOURCE_CONTINUE;
-}
-
 static void
 on_uevent (GUdevClient *client,
            const char  *action,
@@ -1715,28 +1607,6 @@ on_uevent (GUdevClient *client,
   if (!g_udev_device_get_property_as_boolean (device, "HOTPLUG"))
     return;
 
-  if (manager_kms->handle_hotplug_timeout)
-    {
-      g_source_remove (manager_kms->handle_hotplug_timeout);
-      manager_kms->handle_hotplug_timeout = 0;
-    }
-
-  /*
-   * On a hot-plug event, the EDID of one or more connectors might not yet be
-   * ready at this point, resulting in invalid configuration potentially being
-   * applied. Avoid this by first checking whether the EDID is ready at this
-   * point, or otherwise wait a bit and try again.
-   */
-  manager_kms->read_edid_tries = 0;
-  if (has_pending_edid_blob (manager_kms))
-    {
-      manager_kms->handle_hotplug_timeout =
-        g_timeout_add (EDID_RETRY_TIMEOUT_MS,
-                       handle_hotplug_event_timeout,
-                       manager);
-      return;
-    }
-
   handle_hotplug_event (manager);
 }