Subject: [PATCH v5 2/3] hwrng: arm_smccc_trng: Register as an auxiliary device

From: "Aneesh Kumar K.V (Arm)" <[email-masked]>
Date: Thu, 14 May 2026 15:10:29 +0530

The SMCCC TRNG interface is a firmware-provided function rather than a
standalone platform device. Register it as an auxiliary device under the
arm-smccc platform device and convert the hwrng driver to an auxiliary
driver.

This keeps the TRNG device tied to the SMCCC core device while preserving
module autoloading through the auxiliary device ID table.

The conversion changes the device path from the old platform device path,
but no userspace dependency on that path was found. This was confirmed with
a Debian Code Search lookup for the existing platform device name/path.

Signed-off-by: Aneesh Kumar K.V (Arm) <[email-masked]>
---
 drivers/char/hw_random/arm_smccc_trng.c | 25 ++++++++++++++-----------
 drivers/firmware/smccc/smccc.c          | 24 +++++++++++++-----------
 2 files changed, 27 insertions(+), 22 deletions(-)

diff --git a/drivers/char/hw_random/arm_smccc_trng.c b/drivers/char/hw_random/arm_smccc_trng.c
index dcb8e7f37f25..5d56fcbcefa0 100644
--- a/drivers/char/hw_random/arm_smccc_trng.c
+++ b/drivers/char/hw_random/arm_smccc_trng.c
@@ -16,7 +16,7 @@
 #include <linux/device.h>
 #include <linux/hw_random.h>
 #include <linux/module.h>
-#include <linux/platform_device.h>
+#include <linux/auxiliary_bus.h>
 #include <linux/arm-smccc.h>
 
 #ifdef CONFIG_ARM64
@@ -94,29 +94,32 @@ static int smccc_trng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	return copied;
 }
 
-static int smccc_trng_probe(struct platform_device *pdev)
+static int smccc_trng_probe(struct auxiliary_device *adev,
+		const struct auxiliary_device_id *id)
 {
 	struct hwrng *trng;
 
-	trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
+	trng = devm_kzalloc(&adev->dev, sizeof(*trng), GFP_KERNEL);
 	if (!trng)
 		return -ENOMEM;
 
 	trng->name = "smccc_trng";
 	trng->read = smccc_trng_read;
 
-	return devm_hwrng_register(&pdev->dev, trng);
+	return devm_hwrng_register(&adev->dev, trng);
 }
 
-static struct platform_driver smccc_trng_driver = {
-	.driver = {
-		.name		= "smccc_trng",
-	},
-	.probe		= smccc_trng_probe,
+static const struct auxiliary_device_id smccc_trng_id_table[] = {
+	{ .name =  KBUILD_MODNAME ".smccc_trng" },
+	{}
 };
-module_platform_driver(smccc_trng_driver);
+MODULE_DEVICE_TABLE(auxiliary, smccc_trng_id_table);
 
-MODULE_ALIAS("platform:smccc_trng");
+static struct auxiliary_driver smccc_trng_driver = {
+	.probe	  = smccc_trng_probe,
+	.id_table = smccc_trng_id_table,
+};
+module_auxiliary_driver(smccc_trng_driver);
 MODULE_AUTHOR("Andre Przywara");
 MODULE_DESCRIPTION("Arm SMCCC TRNG firmware interface support");
 MODULE_LICENSE("GPL");
diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
index eb077b9aa6da..49ac8172def4 100644
--- a/drivers/firmware/smccc/smccc.c
+++ b/drivers/firmware/smccc/smccc.c
@@ -10,6 +10,7 @@
 #include <linux/arm-smccc.h>
 #include <linux/kernel.h>
 #include <linux/platform_device.h>
+#include <linux/auxiliary_bus.h>
 #include <asm/archrandom.h>
 
 #include "rmm.h"
@@ -94,20 +95,21 @@ static int __init smccc_devices_init(void)
 					PLATFORM_DEVID_NONE, NULL, 0);
 	if (IS_ERR(pdev)) {
 		pr_err("arm-smccc: could not register device: %ld\n", PTR_ERR(pdev));
-	} else {
-		/*
-		 * Register the RMI and RSI devices only when firmware exposes
-		 * the required SMCCC function IDs at a supported revision.
-		 */
-		register_rsi_device(pdev);
+		return 0;
 	}
+	/*
+	 * Register the RMI and RSI devices only when firmware exposes
+	 * the required SMCCC function IDs at a supported revision.
+	 */
+	register_rsi_device(pdev);
 
 	if (smccc_trng_available) {
-		pdev = platform_device_register_simple("smccc_trng", -1,
-						       NULL, 0);
-		if (IS_ERR(pdev))
-			pr_err("smccc_trng: could not register device: %ld\n",
-			       PTR_ERR(pdev));
+		struct auxiliary_device *adev;
+
+		adev = __devm_auxiliary_device_create(&pdev->dev,
+					"arm_smccc_trng", "smccc_trng", NULL, 0);
+		if (!adev)
+			pr_err("smccc_trng: could not register device\n");
 	}
 
 	return 0;
-- 
2.43.0