[PATCH v5 0/2] media: ipu-bridge: survive module unload and reuse the software nodes on rebind

[D. Manresa]

Hello,

v5 fixes a reference counting bug that 2/2 had in v4, and carries
Fernando Rimoli's Tested-by on 1/2.

A correction before anything else: in v4 I wrote that the Surface Pro 7+
was leaving my hands and that the patches were compile-tested only. It
is still here for a few more days, so this version is tested on it.

2/2 as posted in v4 dropped the reference software_node_find_by_name()
takes, on the grounds that the node is never unregistered. That is the
wrong half of the story. software_node_notify() resolves a device's
software node through dev_fwnode(dev)->secondary, which the IPU does not
have yet when device_add() calls it, so it takes no reference;
software_node_notify_remove() does resolve it on the next device_del()
and calls swnode_put(). The reuse path has to hand its reference to that
put.

Measured on the Pro 7+ with a module that reads the kobject reference
count of the INT343E node directly:

  v4 2/2 as posted   4 -> 3 -> 2 -> 1, and the node is gone from
                     /sys/kernel/software_nodes on the fourth
                     remove/rescan cycle. Reproduced twice.
  v5 2/2             4 -> 3 on each PCI remove, back to 4 on each
                     bind, over 16 cycles, children intact.

The decrement happens at the PCI remove, not at the module unload, and
only the IPU node is affected: the sensors' own nodes (INT33BE-4,
INT347A-1, INT347E-5 here) hold steady, since those devices are never
deleted. A remove that follows a failed bind costs nothing, because
there is no secondary fwnode left for software_node_notify_remove() to
resolve.

The series itself, on a Surface Pro 7+ (IPU6 Tiger Lake, 8086:9a19 at
0000:00:05.0, OV5693 + OV8865 + OV7251) running 6.19 with the equivalent
change:

 - without the series, the PCI remove -> modprobe -r -> rescan ->
   modprobe sequence fails exactly as the 2/2 commit message describes,
   with -EEXIST, and the cameras stay dead until a reboot;
 - with it, four cycles complete and all three sensors stream after
   each one.

Two things that cost me time, in case they would cost a reviewer the
same:

 - modprobe -r intel_ipu6_isys intel_ipu6 leaves ipu_bridge resident at
   reference count 0. Without an explicit modprobe -r ipu_bridge the
   module image is never freed and neither failure reproduces.
 - the reuse path logs at dev_dbg(), so it is invisible without
   dyndbg=+p.

The asymmetry underneath this is in drivers/base, not here: a software
node that becomes a device's secondary fwnode after device_add() gets a
swnode_put() at device_del() that no swnode_get() ever matched. I am
accounting for it in the bridge because that is where this series is,
but if it should be balanced in software_node_notify() instead, say so
and I will send that.

Unrelated but worth flagging: Sergey Lebedev's "Add the Surface Pro 11
infrared illuminator" series touches the same two lines 1/2 does
(dev_properties[3] and the "lens-focus" name), so whichever of the two
lands second needs a trivial rebase.

Changes since v4:
 - 2/2: keep the reference from software_node_find_by_name() instead of
   dropping it, and say in the comment what consumes it;
 - 2/2: commit message notes the reference counting;
 - 1/2: Fernando Rimoli's Tested-by (Surface Pro 9);
 - tested on hardware, where v4 was compile-tested only.

Changes since v3:
 - 1/2 and 2/2: commit messages cut down;
 - 1/2: lens_focus moved into struct ipu_property_names and link_freqs
   into struct ipu_sensor;
 - 2/2: reuse-path comment shortened.

v4: https://lore.kernel.org/linux-media/20261010155626.2766298-1-dmanresa@xxxxxxxxx/
v3: https://lore.kernel.org/linux-media/20261008132614.2456716-1-dmanresa@xxxxxxxxx/

Thanks,
D. Manresa

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

 drivers/media/pci/intel/ipu-bridge.c | 34 +++++++++++++++++++++++++++++++---
 include/media/ipu-bridge.h           |  6 ++++++
 2 files changed, 37 insertions(+), 3 deletions(-)

-- 
2.43.0