Re: [PATCH 26/37] drm: event-notifier: add mechanism to notify about hotplug events

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] Global blocking notifier chain couples independent DRM devices.
- [Low] Missing forward declaration for `struct notifier_block` in header.
- [Low] Kernel-doc mismatch for DRM_BRIDGE_DETACHED enum value.
--

commit 233daf5d4ef6810bfafb5fb5ba8829a7db6987d3
Author: Luca Ceresoli <luca.ceresoli@bootlin.com>

drm: event-notifier: add mechanism to notify about hotplug events

This patch introduces a DRM event notifier to allow interested parties
to be notified about bridge hotplug events. It adds a new common file
implementing the notifier and defines initial events for bridge detach
and MIPI DSI attach.

> diff --git a/drivers/gpu/drm/drm_event_notifier.c b/drivers/gpu/drm/drm_event_notifier.c
> new file mode 100644
> index 0000000000000..76af4dd4cdb02
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_event_notifier.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Internal event notifier for DRM drivers
> + *
> + * Copyright (C) 2026 GE HealthCare
> + * Author: Luca Ceresoli <luca.ceresoli@bootlin.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/notifier.h>
> +
> +#include <drm/drm_event_notifier.h>
> +
> +static BLOCKING_NOTIFIER_HEAD(drm_event_notifier);

Does using a single, global blocking notifier for all DRM hotplug events risk
coupling independent DRM devices?

When an event occurs on one device, it appears this will trigger callbacks for
every registered listener across the entire system. Could this lead to
cross-device lock contention, or cause listeners on unrelated hardware to
unexpectedly react to the event?

[ ... ]

> diff --git a/include/drm/drm_event_notifier.h b/include/drm/drm_event_notifier.h
> new file mode 100644
> index 0000000000000..78afc014ec9a6
> --- /dev/null
> +++ b/include/drm/drm_event_notifier.h
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Internal event notifier for DRM drivers
> + *
> + * Copyright (C) 2026 GE HealthCare
> + * Author: Luca Ceresoli <luca.ceresoli@bootlin.com>
> + */
> +
> +#ifndef _DRM_EVENT_NOTIFIER_H_
> +#define _DRM_EVENT_NOTIFIER_H_
> +
> +/**
> + * enum drm_event_notifier_event - DRM bridge events
> + */
> +enum drm_event_notifier_event {
> +	/**
> +	 * @DRM_MIPI_DSI_ATTACHED: A MIPI DSI device has just been attached
> +	 * to its MIPI DSI host. @data is a pointer to the &struct
> +	 * mipi_dsi_device that has just attached.
> +	 */
> +	DRM_MIPI_DSI_ATTACHED,
> +	/**
> +	 * @DRM_BRIDGE_NOTIFY_DETACHED: A bridge has just been detached

This isn't a bug, but the kernel-doc references @DRM_BRIDGE_NOTIFY_DETACHED
while the actual enum value is DRM_BRIDGE_DETACHED. Will this cause warnings
during documentation builds?

> +	 * from the encoder bridge chain. Emitted at the end of
> +	 * drm_bridge_detach(), after removing the bridge from the encoder
> +	 * chain. @data is a pointer to the &struct drm_bridge that has
> +	 * just been detached.
> +	 */
> +	DRM_BRIDGE_DETACHED,
> +};
> +
> +int drm_event_notifier_register(struct notifier_block *nb);

Should there be a forward declaration for struct notifier_block here, or an
include for <linux/notifier.h>?

Without it, files including this header might get compiler warnings about the
struct being declared inside a parameter list, since kernel headers are
typically expected to be self-contained.

> +int drm_event_notifier_unregister(struct notifier_block *nb);
> +void drm_event_notifier_notify(unsigned long event, void *data);
> +
> +#endif /* _DRM_EVENT_NOTIFIER_H_ */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260519-drm-bridge-hotplug-v1-0-45e2bdb3dfb4@bootlin.com?part=26