[PATCH] of/irq: Add msi-parent check to of_msi_xlate()

Lorenzo Pieralisi
2025-09-16T09:19:11Z

In some legacy platforms the MSI controller for a PCI host
bridge is identified by an msi-parent property whose phandle
points at an MSI controller node with no #msi-cells property,
that implicitly means #msi-cells == 0.

For such platforms, mapping a device ID and retrieving the
MSI controller node becomes simply a matter of checking
whether in the device hierarchy there is an msi-parent property
pointing at an MSI controller node with such characteristics.

Add a helper function to of_msi_xlate() to check the msi-parent
property in addition to msi-map and retrieve the MSI controller
node (with a 1:1 ID deviceID-IN<->deviceID-OUT mapping) to
provide support for deviceID mapping and MSI controller node
retrieval for such platforms.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Sascha Bischoff <sascha.bischoff@arm.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
---
drivers/of/irq.c | 38 +++++++++++++++++++++++++++++++++++---
1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/of/irq.c b/drivers/of/irq.c
index e7c12abd10ab..d0e2dfd0ee28 100644
--- a/drivers/of/irq.c
+++ b/drivers/of/irq.c
@@ -670,6 +670,35 @@ void __init of_irq_init(const struct of_device_id *matches)
}
}

+static int of_check_msi_parent(struct device_node *dev_node, struct device_node **msi_node)
+{
+ struct of_phandle_args msi_spec;
+ int ret;
+
+ /*
+ * An msi-parent phandle with a missing or == 0 #msi-cells
+ * property identifies a 1:1 ID translation mapping.
+ *
+ * Set the msi controller node if the firmware matches this
+ * condition.
+ */
+ ret = of_parse_phandle_with_optional_args(dev_node, "msi-parent", "#msi-cells",
+ 0, &msi_spec);
+ if (!ret) {
+ if ((*msi_node && *msi_node != msi_spec.np) || msi_spec.args_count != 0)
+ ret = -EINVAL;
+
+ if (!ret) {
+ /* Return with a node reference held */
+ *msi_node = msi_spec.np;
+ return 0;
+ }
+ of_node_put(msi_spec.np);
+ }
+
+ return ret;
+}
+
/**
* of_msi_xlate - map a MSI ID and find relevant MSI controller node
* @dev: device for which the mapping is to be done.
@@ -677,7 +706,7 @@ void __init of_irq_init(const struct of_device_id *matches)
* @id_in: Device ID.
*
* Walk up the device hierarchy looking for devices with a "msi-map"
- * property. If found, apply the mapping to @id_in.
+ * or "msi-parent" property. If found, apply the mapping to @id_in.
* If @msi_np points to a non-NULL device node pointer, only entries targeting
* that node will be matched; if it points to a NULL value, it will receive the
* device node of the first matching target phandle, with a reference held.
@@ -691,12 +720,15 @@ u32 of_msi_xlate(struct device *dev, struct device_node **msi_np, u32 id_in)

/*
* Walk up the device parent links looking for one with a
- * "msi-map" property.
+ * "msi-map" or an "msi-parent" property.
*/
- for (parent_dev = dev; parent_dev; parent_dev = parent_dev->parent)
+ for (parent_dev = dev; parent_dev; parent_dev = parent_dev->parent) {
if (!of_map_id(parent_dev->of_node, id_in, "msi-map",
"msi-map-mask", msi_np, &id_out))
break;
+ if (!of_check_msi_parent(parent_dev->of_node, msi_np))
+ break;
+ }
return id_out;
}

--
2.48.0