linux-kernel - [PATCH] of/irq: Add msi-parent check to of_msi

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Message-ID: <20250916091858.257868-1-lpieralisi@kernel.org>
Date: Tue, 16 Sep 2025 11:18:58 +0200
From: Lorenzo Pieralisi <lpieralisi@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org,
	Sascha Bischoff <sascha.bischoff@....com>,
	Rob Herring <robh@...nel.org>,
	Marc Zyngier <maz@...nel.org>
Subject: [PATCH] of/irq: Add msi-parent check to of_msi_xlate()

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@...nel.org>
Cc: Sascha Bischoff <sascha.bischoff@....com>
Cc: Rob Herring <robh@...nel.org>
Cc: Marc Zyngier <maz@...nel.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