terminal: fix mode sync for connectors

The GETXY ioctls of DRM are usually called twice by libdrm: Once to
retrieve the number of objects, a second time with suitably sized buffers
to actually retrieve all objects. In grdrm, we avoid these excessive calls
and instead just call ioctls with cached buffers and resize them if they
were too small.

However, connectors need to read the mode list via EDID, which is horribly
slow. As the kernel still cannot do that asynchronously (seriously, we
need to fix this!), it has a hack to only do it if count_modes==0. This is
fine with libdrm, as it calls every ioctl twice, anyway. However, we fail
horribly with this as we usually never pass 0.

Fix this by calling into GETCONNECTOR ioctls twice in case we received an
hotplug event. Only in those cases, we need to re-read modes, so this
should be totally fine.

1 files changed, 24 insertions, 9 deletions

diff --git a/src/libsystemd-terminal/grdev-drm.c b/src/libsystemd-terminal/grdev-drm.c
index 5cebb0609e..2e55ad326b 100644
--- a/src/libsystemd-terminal/grdev-drm.c
+++ b/src/libsystemd-terminal/grdev-drm.c
@@ -264,6 +264,7 @@ struct grdrm_card {
         Hashmap *object_map;
 
         bool async_hotplug : 1;
+        bool hotplug : 1;
         bool running : 1;
         bool ready : 1;
         bool cap_dumb : 1;
@@ -603,12 +604,19 @@ static int grdrm_connector_resync(grdrm_connector *connector) {
                 res.count_encoders = connector->kern.max_encoders;
                 res.count_props = connector->kern.max_props;
 
-                /* Retrieve modes only if we have none. This avoids expensive
-                 * EDID reads in the kernel, that can slow down resyncs
-                 * considerably! */
-                if (connector->kern.n_modes == 0) {
-                        res.modes_ptr = PTR_TO_UINT64(connector->kern.modes);
-                        res.count_modes = connector->kern.max_modes;
+                /* The kernel reads modes from the EDID information only if we
+                 * pass count_modes==0. This is a legacy hack for libdrm (which
+                 * called every ioctl twice). Now we have to adopt.. *sigh*.
+                 * If we never received an hotplug event, there's no reason to
+                 * sync modes. EDID reads are heavy, so skip that if not
+                 * required. */
+                if (card->hotplug) {
+                        if (tries > 0) {
+                                res.modes_ptr = PTR_TO_UINT64(connector->kern.modes);
+                                res.count_modes = connector->kern.max_modes;
+                        } else {
+                                resized = true;
+                        }
                 }
 
                 r = ioctl(card->fd, DRM_IOCTL_MODE_GETCONNECTOR, &res);
@@ -689,7 +697,6 @@ static int grdrm_connector_resync(grdrm_connector *connector) {
                         continue;
 
                 connector->kern.n_encoders = res.count_encoders;
-                connector->kern.n_modes = res.count_modes;
                 connector->kern.n_props = res.count_props;
                 connector->kern.type = res.connector_type;
                 connector->kern.type_id = res.connector_type_id;
@@ -698,6 +705,8 @@ static int grdrm_connector_resync(grdrm_connector *connector) {
                 connector->kern.mm_width = res.mm_width;
                 connector->kern.mm_height = res.mm_height;
                 connector->kern.subpixel = res.subpixel;
+                if (res.modes_ptr == PTR_TO_UINT64(connector->kern.modes))
+                        connector->kern.n_modes = res.count_modes;
 
                 break;
         }
@@ -2167,6 +2176,7 @@ static void grdrm_card_hotplug(grdrm_card *card) {
 
         grdrm_card_configure(card);
         card->ready = true;
+        card->hotplug = false;
 
         grdev_session_unpin(card->base.session);
 }
@@ -2374,6 +2384,7 @@ static int grdrm_card_open(grdrm_card *card, int dev_fd) {
 
         sd_event_source_set_enabled(card->fd_src, SD_EVENT_OFF);
 
+        card->hotplug = true;
         card->fd = fd;
         fd = -1;
 
@@ -3029,13 +3040,17 @@ void grdev_drm_card_hotplug(grdev_card *basecard, struct udev_device *ud) {
                 /* If we get add/remove events on DRM nodes without devnum, we
                  * got hotplugged DRM objects so refresh the device. */
                 devnum = udev_device_get_devnum(ud);
-                if (devnum == 0)
+                if (devnum == 0) {
+                        card->hotplug = true;
                         grdrm_card_hotplug(card);
+                }
         } else if (streq_ptr(action, "change")) {
                 /* A change event with HOTPLUG=1 is sent whenever a connector
                  * changed state. Refresh the device to update our state. */
                 p = udev_device_get_property_value(ud, "HOTPLUG");
-                if (streq_ptr(p, "1"))
+                if (streq_ptr(p, "1")) {
+                        card->hotplug = true;
                         grdrm_card_hotplug(card);
+                }
         }
 }