[PATCH RESEND v7 0/2] Pass down hot-plug CONNECTOR ID to user-space

Nicolas Frattaroli
2026-04-15T18:00:29Z

I will be taking over this series from Marius Vlad.

This series addresses a shortcoming whereby a hot plug event is sent
without it being passed the actual connector that caused it. This takes
into consideration both the polling path and the HPD (Hot Plug Detect)
path. It also adds support for the vkms driver (using ConfigFS) for
propagating the connector ID when changing the connector's status.

The motivation is that user-space applications such as Weston would
previously receive non-connector-specific hotplug events, and then have
to figure out themselves which connector needs to have a modeset
executed on. This notably did not work when the hotplug events came in
too fast, resulting in Weston missing an on-off-on transition of a
connector, seeing that its state was unchanged from "on" so can't be the
one that was hotplugged, and skipping reinitialising it as it looks
through the other connectors that could've caused it.

The real world implication is that on setups with slightly sketchy HDMI
connections, a brief flicker in the HPD signal could result in video
output bidding farewell entirely until a manual proper re-plug was
performed.

By sending connector specific hotplug events, this ambiguity is
resolved without any change to the user-space API.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
Changes in v7 RESEND:
- None, other than removing the leftover diffstat from the cover letter
- Link to v7: https://lore.kernel.org/r/20260217-hot-plug-passup-v7-0-f8221b2aab51@collabora.com

Changes in v7:
- Drop the two vkms patches, as I don't want them to be blocked on
review. I still think they're correct, but they're not essential and
don't need to block this series.
- Link to v6: https://lore.kernel.org/r/20260123-hot-plug-passup-v6-0-aaaf61d960bb@collabora.com

Changes in v6:
- Rewrote cover letter to explain the motivation for this series more
plainly
- Rename "status_changed" to "pending_hp"
- Set "pending_hp" in the existing path that would also affect
epoch_counter
- No longer set the boolean in drm_helper_probe_single_connector_modes,
as it does not appear to be necessary
- Reword commits to better justify the changes
- Link to v5: https://lore.kernel.org/r/20251111162338.15141-1-marius.vlad@collabora.com/

Changes in v5:
- vkms: add support for sending the CONNECTOR ID when hot-plugging through
ConfigFS - as reported by Louis, vkms can now make use of ConfigFS to
simulate connector status.
- vkms: add a small change to ignore previous/old drm connector status
when sending out hot-plug uevent.
- Link to v4: https://lore.kernel.org/r/20251103174558.7709-1-marius.vlad@collabora.com/

Changes in v4:
- removed the "This patch" bit - Dmitry
- added a short note when the flag is set and cleared - Dmitry
- address double dead-locking detected - kbot: https://lore.kernel.org/dri-devel/202509251410.fdfbcac3-lkp@intel.com/
- virtual connectors do not seem have any kind of hotplug - added
polling in vkms - as noted by Ian
- Link to v3: https://lore.kernel.org/r/20250923083636.4749-1-marius.vlad@collabora.com/

Changes in v3:
- Address comments from Dmitry:
- guard connector status write with mode_config.mutex
- avoid setting up the connector status and immediately unset it. Do the
unset in drm_kms_helper_hotplug_event/drm_kms_helper_connector_hotplug_event
- Link to v2: https://lore.kernel.org/r/20250729165708.9947-1-marius.vlad@collabora.com/

Changes in v2:
- Address comments from Daniel:
- split patch into 2, one that introduces a bool to track connector
connection status change and a patch that uses that to be able to send
hot plug events with the proper CONNECTOR ID to udev and further pass
that down to user-space
- nuke out mutex when iterating connector list
- fix typo
- Link to v1: https://lore.kernel.org/r/20250627131751.2004-1-marius.vlad@collabora.com/

---
Marius Vlad (2):
drm: Introduce pending_hp to drm_connector
drm: Send per-connector hotplug events

drivers/gpu/drm/drm_connector.c | 1 +
drivers/gpu/drm/drm_probe_helper.c | 39 +++++++++++++++++++++++++++++++++-----
drivers/gpu/drm/drm_sysfs.c | 2 ++
include/drm/drm_connector.h | 3 +++
4 files changed, 40 insertions(+), 5 deletions(-)
---
base-commit: 4c59525db84aca677fd9f052e662912ad9d88448
change-id: 20260121-hot-plug-passup-f8ed03f7c202

Best regards,
--
Nicolas Frattaroli <nicolas.frattaroli@collabora.com>