[PATCH 0/2] media: ipu-bridge: survive module unload and reuse the software nodes on rebind

[D. Manresa]

Hello,

This implements what was agreed in the "ipu-bridge: software nodes are
never unregistered" thread [1]: the software nodes are deliberately
leaked and cannot be removed (circular remote-endpoint references), so
instead of a teardown, make the two halves of the intended design work -
the nodes must actually survive module unload, and a rebind must reuse
them instead of failing.

[1/2] makes the registered properties self-contained in the never-freed
bridge allocation. One correction to my original report: the property
name strings I pointed at (prop_names) were never a problem - struct
ipu_property_names holds char arrays, so those are already copied. The
real module-image references were the "link-frequencies" property
values (pointing into the ipu_supported_sensors[] rodata) and the
"lens-focus" property name string literal. The link-frequencies one is
directly observable on hardware: with the creator module unloaded, a
re-probing sensor reads poisoned frequencies ("supported link freq
419200000ll not found"); reloading the module - which puts identical
rodata back at the same address - makes the same probe succeed again.

[2/2] adds the reuse path to ipu_bridge_init(): if the IPU HID node is
already registered, point the IPU's secondary fwnode at it and return.
The sensors' ACPI fwnodes keep their secondary pointers from the first
bind (nothing clears them), and with [1/2] the nodes they point at are
still valid.

Tested on a Surface Pro 7+ (IPU6 Tiger Lake, OV5693 + OV8865 + OV7251):
the PCI remove -> module unload -> rescan -> modprobe sequence from the
report, which today is fatal until reboot (-EEXIST), completes cleanly
with this series - "Reusing the previously registered software nodes" -
twice in a row, with all three cameras streaming after each rebind. Also
re-verified per Sakari's question that the failure is identical when all
sensor sub-device drivers are unbound before the PCI remove (answered
with the data in [1]).

The series was developed with the assistance of an AI tool (Claude) and
verified on the hardware described above.

Thanks,
D. Manresa

D. Manresa (2):
  media: ipu-bridge: don't reference the module image from the software
    nodes
  media: ipu-bridge: reuse the software nodes on rebind

 drivers/media/pci/intel/ipu-bridge.c | 38 ++++++++++++++++++++++++++---
 include/media/ipu-bridge.h           |  9 +++++++++
 2 files changed, 44 insertions(+), 3 deletions(-)

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2.43.0