[PATCH 2/4] platform/x86/amd/hsmp: Add /sys/devices/amd_hsmp socket devices

[Erwan Velu <erwanaliasr1@gmail.com>]

From: Erwan Velu <e.velu@criteo.com>

The per-socket attributes live under /sys/devices/platform/AMDI0097:0X
with the ACPI driver, while the platform driver uses
/sys/devices/platform/amd_hsmp/socketN. Userspace has to know which
driver probed to find them.

Add a driver-independent /sys/devices/amd_hsmp/socketN device per
socket carrying hsmp_sock_groups, and register it from the ACPI driver.
The AMDI0097:0X attributes are kept, as they are documented ABI.

The socket device is unregistered before remove takes hsmp_sock_rwsem:
device_unregister() waits for in-flight sysfs reads, which take the
rwsem for read.

Assisted-by: claude-opus-5-5
Signed-off-by: Erwan Velu <e.velu@criteo.com>
---
 Documentation/arch/x86/amd_hsmp.rst   |   8 +-
 drivers/platform/x86/amd/hsmp/acpi.c  |   6 ++
 drivers/platform/x86/amd/hsmp/hsmp.h  |   5 ++
 drivers/platform/x86/amd/hsmp/sysfs.c | 112 +++++++++++++++++++++++++-
 4 files changed, 129 insertions(+), 2 deletions(-)

diff --git a/Documentation/arch/x86/amd_hsmp.rst b/Documentation/arch/x86/amd_hsmp.rst
index fa1fc240e212..aba4a009bd8d 100644
--- a/Documentation/arch/x86/amd_hsmp.rst
+++ b/Documentation/arch/x86/amd_hsmp.rst
@@ -57,6 +57,12 @@ In-kernel integration:
 HSMP sysfs interface
 ====================
 
+The ACPI driver exposes its per socket sysfs files in a per socket
+directory created at /sys/devices/amd_hsmp/socket%d/.
+
+For backward compatibility, the files are also available under
+/sys/devices/platform/AMDI0097:0X/.
+
 1. Metrics table binary sysfs
 
 AMD MI300A MCM provides GET_METRICS_TABLE message to retrieve
@@ -80,7 +86,7 @@ The same is defined in the amd_hsmp.h header.
 
 2. HSMP telemetry sysfs files
 
-Following sysfs files are available at /sys/devices/platform/AMDI0097:0X/.
+Following sysfs files are available at /sys/devices/amd_hsmp/socket%d/.
 
 * c0_residency_input: Percentage of cores in C0 state.
 * prochot_status: Reports 1 if the processor is at thermal threshold value,
diff --git a/drivers/platform/x86/amd/hsmp/acpi.c b/drivers/platform/x86/amd/hsmp/acpi.c
index d76979baffa8..468d4b1515db 100644
--- a/drivers/platform/x86/amd/hsmp/acpi.c
+++ b/drivers/platform/x86/amd/hsmp/acpi.c
@@ -441,6 +441,10 @@ static int hsmp_acpi_probe(struct platform_device *pdev)
 		dev_dbg(&pdev->dev, "AMD HSMP ACPI misc device registered\n");
 	}
 
+	ret = hsmp_sock_dev_register(dev_get_drvdata(&pdev->dev));
+	if (ret)
+		dev_warn(&pdev->dev, "Failed to register HSMP socket device: %d\n", ret);
+
 	return 0;
 }
 
@@ -448,6 +452,8 @@ static void hsmp_acpi_remove(struct platform_device *pdev)
 {
 	struct hsmp_socket *sock = dev_get_drvdata(&pdev->dev);
 
+	hsmp_sock_dev_unregister(sock);
+
 	/*
 	 * Serialize the kref_put() and any release it triggers against a
 	 * concurrent probe, and drain the data plane for the whole
diff --git a/drivers/platform/x86/amd/hsmp/hsmp.h b/drivers/platform/x86/amd/hsmp/hsmp.h
index 692721e2e6d3..f638edd7768b 100644
--- a/drivers/platform/x86/amd/hsmp/hsmp.h
+++ b/drivers/platform/x86/amd/hsmp/hsmp.h
@@ -28,6 +28,7 @@
 
 #define HSMP_CDEV_NAME		"hsmp_cdev"
 #define HSMP_DEVNODE_NAME	"hsmp"
+#define HSMP_ROOT_DEV_NAME	"amd_hsmp"
 #define ACPI_HSMP_DEVICE_HID    "AMDI0097"
 
 #define DRIVER_VERSION		"2.6"
@@ -47,6 +48,7 @@ struct hsmp_socket {
 	/* Size of the region mapped at @metric_tbl_addr, as reported by SMU */
 	size_t metric_tbl_size;
 	void __iomem *virt_base_addr;
+	struct device *sysfs_dev;
 	struct semaphore hsmp_sem;
 	/* Serializes HSMP_GET_METRIC_TABLE fill-and-copy for this socket */
 	struct mutex metric_read_lock;
@@ -80,6 +82,9 @@ int hsmp_create_sensor(struct device *dev, u16 sock_ind);
 static inline int hsmp_create_sensor(struct device *dev, u16 sock_ind) { return 0; }
 #endif
 int hsmp_msg_get_nargs(u16 sock_ind, u32 msg_id, u32 *data, u8 num_args);
+int hsmp_sock_dev_register(struct hsmp_socket *sock);
+void hsmp_sock_dev_unregister(struct hsmp_socket *sock);
+
 extern const struct attribute_group *hsmp_sock_groups[];
 
 /*
diff --git a/drivers/platform/x86/amd/hsmp/sysfs.c b/drivers/platform/x86/amd/hsmp/sysfs.c
index b1db3b4d77b9..e9e91b640b2a 100644
--- a/drivers/platform/x86/amd/hsmp/sysfs.c
+++ b/drivers/platform/x86/amd/hsmp/sysfs.c
@@ -4,7 +4,8 @@
  * Copyright (c) 2024, AMD.
  * All Rights Reserved.
  *
- * This file provides the per-socket sysfs attributes of the HSMP interface.
+ * This file provides the per-socket sysfs attributes of the HSMP interface
+ * and the /sys/devices/amd_hsmp/socket%u devices carrying them.
  */
 
 #include <asm/amd/hsmp.h>
@@ -12,7 +13,12 @@
 #include <linux/array_size.h>
 #include <linux/bitfield.h>
 #include <linux/bits.h>
+#include <linux/cleanup.h>
 #include <linux/device.h>
+#include <linux/err.h>
+#include <linux/lockdep.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
 #include <linux/sysfs.h>
 
 #include "hsmp.h"
@@ -336,3 +342,107 @@ const struct attribute_group *hsmp_sock_groups[] = {
 	NULL
 };
 EXPORT_SYMBOL_NS_GPL(hsmp_sock_groups, "AMD_HSMP");
+
+/*
+ * /sys/devices/amd_hsmp is created when the first socket device is registered
+ * and removed with the last one. hsmp_root_lock serializes that against the
+ * per-socket register/unregister calls.
+ */
+static DEFINE_MUTEX(hsmp_root_lock);
+static struct device *hsmp_root_dev;
+static unsigned int hsmp_root_users;
+
+static void hsmp_sock_dev_release(struct device *dev)
+{
+	kfree(dev);
+}
+
+/**
+ * hsmp_sock_dev_register() - Create /sys/devices/amd_hsmp/socket%u for @sock.
+ * @sock: fully probed HSMP socket.
+ *
+ * The device carries hsmp_sock_groups with @sock as its drvdata, so @sock must
+ * stay valid until hsmp_sock_dev_unregister() returns.
+ *
+ * Return: 0 on success, a negative error code otherwise.
+ */
+int hsmp_sock_dev_register(struct hsmp_socket *sock)
+{
+	struct device *dev;
+	int ret;
+
+	guard(mutex)(&hsmp_root_lock);
+
+	if (!hsmp_root_users) {
+		hsmp_root_dev = root_device_register(HSMP_ROOT_DEV_NAME);
+		if (IS_ERR(hsmp_root_dev)) {
+			ret = PTR_ERR(hsmp_root_dev);
+			hsmp_root_dev = NULL;
+			return ret;
+		}
+	}
+
+	/*
+	 * Built by hand rather than with device_create_with_groups(), which
+	 * rejects a NULL class: these devices belong to no class or bus.
+	 */
+	dev = kzalloc_obj(*dev);
+	if (!dev) {
+		ret = -ENOMEM;
+		goto err_root;
+	}
+
+	device_initialize(dev);
+	dev->parent = hsmp_root_dev;
+	dev->groups = hsmp_sock_groups;
+	dev->release = hsmp_sock_dev_release;
+	dev_set_drvdata(dev, sock);
+
+	ret = dev_set_name(dev, "socket%u", sock->sock_ind);
+	if (!ret)
+		ret = device_add(dev);
+	if (ret) {
+		put_device(dev);
+		goto err_root;
+	}
+
+	sock->sysfs_dev = dev;
+	hsmp_root_users++;
+
+	return 0;
+
+err_root:
+	if (!hsmp_root_users) {
+		root_device_unregister(hsmp_root_dev);
+		hsmp_root_dev = NULL;
+	}
+	return ret;
+}
+EXPORT_SYMBOL_NS_GPL(hsmp_sock_dev_register, "AMD_HSMP");
+
+/**
+ * hsmp_sock_dev_unregister() - Remove /sys/devices/amd_hsmp/socket%u for @sock.
+ * @sock: HSMP socket; a no-op if its device was never registered.
+ *
+ * device_unregister() waits for in-flight show/read handlers, which take
+ * hsmp_sock_rwsem for read. The caller must therefore not hold it, or a
+ * concurrent sysfs read would deadlock the teardown.
+ */
+void hsmp_sock_dev_unregister(struct hsmp_socket *sock)
+{
+	lockdep_assert_not_held(&hsmp_sock_rwsem);
+
+	guard(mutex)(&hsmp_root_lock);
+
+	if (!sock->sysfs_dev)
+		return;
+
+	device_unregister(sock->sysfs_dev);
+	sock->sysfs_dev = NULL;
+
+	if (!--hsmp_root_users) {
+		root_device_unregister(hsmp_root_dev);
+		hsmp_root_dev = NULL;
+	}
+}
+EXPORT_SYMBOL_NS_GPL(hsmp_sock_dev_unregister, "AMD_HSMP");
-- 
2.53.0