[PATCH v2 2/2] media: ipu-bridge: reuse the software nodes on rebind

[D. Manresa]

The software nodes registered by ipu_bridge_init() are deliberately
never unregistered, and the intended design is for a rebind to reuse
the already registered nodes. That reuse path however only exists for
the case where the IPU device kept its secondary fwnode link, which the
fwnode graph check at the top of ipu_bridge_init() detects: then the
function returns early. When the link is gone, ipu_bridge_init()
unconditionally registers the IPU HID software node again, which fails
with -EEXIST on the sysfs name (the node from the previous bind is
still registered) and the IPU driver fails to probe.

That is exactly what happens when the IPU PCI device is removed and
re-scanned: device_del() unsets the ACPI companion, and
set_primary_fwnode(dev, NULL) then clears the ACPI fwnode's ->secondary
pointer, so the fwnode graph check on the next probe finds no endpoints
and falls through to registration. Observed on a Surface Pro 7+ (IPU6):

  echo 1 > /sys/bus/pci/devices/0000:00:05.0/remove
  modprobe -r intel_ipu6_isys intel_ipu6   # ipu-bridge unloads too
  echo 1 > /sys/bus/pci/rescan
  modprobe intel_ipu6

  sysfs: cannot create duplicate filename '/kernel/software_nodes/INT343E'
  intel-ipu6 0000:00:05.0: Failed to register the IPU HID node
  intel-ipu6: probe of 0000:00:05.0 failed with error -17

after which the cameras are unusable until reboot.

Add the missing reuse path: if the IPU software node is already
registered, look it up with software_node_find_by_name(), point the
device's secondary fwnode at it and return success. That is all a
rebind needs: the sensor, IVSC and VCM links live on devices that
survive an IPU unbind, so nothing has cleared those.

software_node_find_by_name() takes a reference on the node it returns;
drop it right away since the node is kept alive by its never dropped
registration.

Assisted-by: LLM

Fixes: 803abec64ef9 ("media: ipu3-cio2: Add cio2-bridge to ipu3-cio2 driver")
Signed-off-by: D. Manresa <dmanresa@xxxxxxxxx>
---
 drivers/media/pci/intel/ipu-bridge.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/media/pci/intel/ipu-bridge.c b/drivers/media/pci/intel/ipu-bridge.c
index 4de42ed..6fa1c3c 100644
--- a/drivers/media/pci/intel/ipu-bridge.c
+++ b/drivers/media/pci/intel/ipu-bridge.c
@@ -930,6 +930,7 @@ static DEFINE_MUTEX(ipu_bridge_mutex);
 int ipu_bridge_init(struct device *dev,
 		    ipu_parse_sensor_fwnode_t parse_sensor_fwnode)
 {
+	const struct software_node *ipu_node;
 	struct fwnode_handle *fwnode;
 	struct ipu_bridge *bridge;
 	unsigned int i;
@@ -940,6 +941,29 @@ int ipu_bridge_init(struct device *dev,
 	if (!ipu_bridge_check_fwnode_graph(dev_fwnode(dev)))
 		return 0;
 
+	/*
+	 * The software nodes registered by a previous ipu_bridge_init() call
+	 * are deliberately kept registered when the module is unloaded, and
+	 * the sensors' ACPI fwnodes still have them as their secondary
+	 * fwnodes. If the IPU software node is already registered this is a
+	 * rebind, e.g. after the PCI device was removed and re-scanned,
+	 * which drops the IPU's secondary fwnode link. Registering the nodes
+	 * again would fail with -EEXIST, so instead reuse them and just
+	 * restore the IPU's secondary fwnode link.
+	 */
+	ipu_node = software_node_find_by_name(NULL, IPU_HID);
+	if (ipu_node) {
+		fwnode = software_node_fwnode(ipu_node);
+		set_secondary_fwnode(dev, fwnode);
+		/*
+		 * The node stays registered, it does not need the reference
+		 * software_node_find_by_name() took to stay alive.
+		 */
+		fwnode_handle_put(fwnode);
+		dev_dbg(dev, "Reusing the previously registered software nodes\n");
+		return 0;
+	}
+
 	if (!ipu_bridge_ivsc_is_ready())
 		return dev_err_probe(dev, -EPROBE_DEFER,
 				     "waiting for IVSC to become ready\n");
-- 
2.43.0