[PATCH v2 3/3] platform/x86: dell-smbios-wmi: Replace global list with single item

[Armin Wolf <W_Armin@gmx.de>]

There can only exist a single instance of the dell-smbios-wmi driver
at the same time because of naming conflicts with the character
device ("wmi/dell-smbios"). Having a global list for all instances
thus makes no sense.

Replace the global list with a single item used by the character
device. This simplifies the driver and allows us to mark it as
being multi-instance safe.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/platform/x86/dell/dell-smbios-wmi.c | 68 ++++++++++-----------
 1 file changed, 31 insertions(+), 37 deletions(-)

diff --git a/drivers/platform/x86/dell/dell-smbios-wmi.c b/drivers/platform/x86/dell/dell-smbios-wmi.c
index 2108de4e48a3..f9443ddfff55 100644
--- a/drivers/platform/x86/dell/dell-smbios-wmi.c
+++ b/drivers/platform/x86/dell/dell-smbios-wmi.c
@@ -10,7 +10,6 @@
 #include <linux/device.h>
 #include <linux/dmi.h>
 #include <linux/fs.h>
-#include <linux/list.h>
 #include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -34,22 +33,14 @@ struct misc_bios_flags_structure {
 struct wmi_smbios_priv {
 	struct mutex call_lock; /* Protects the content of the SMBIOS buffer */
 	struct dell_wmi_smbios_buffer *buf;
-	struct list_head list;
 	struct wmi_device *wdev;
 	struct device *child;
 	u64 req_buf_size;
 	struct miscdevice char_dev;
 };
 
-static DECLARE_RWSEM(list_lock);	/* Protects access to wmi_list */
-static LIST_HEAD(wmi_list);
-
-static inline struct wmi_smbios_priv *get_first_smbios_priv(void)
-{
-	return list_first_entry_or_null(&wmi_list,
-					struct wmi_smbios_priv,
-					list);
-}
+static DECLARE_RWSEM(chardev_lock);	/* Protects chardev_priv */
+static struct wmi_smbios_priv *chardev_priv;
 
 static int run_smbios_call(struct wmi_device *wdev)
 {
@@ -106,16 +97,13 @@ static int dell_smbios_wmi_call(struct device *dev, struct calling_interface_buf
 static ssize_t dell_smbios_wmi_read(struct file *filp, char __user *buffer, size_t length,
 				    loff_t *offset)
 {
-	struct wmi_smbios_priv *priv;
+	guard(rwsem_read)(&chardev_lock);
 
-	guard(rwsem_read)(&list_lock);
-
-	priv = get_first_smbios_priv();
-	if (!priv)
+	if (!chardev_priv)
 		return -ENODEV;
 
-	return simple_read_from_buffer(buffer, length, offset, &priv->req_buf_size,
-				       sizeof(priv->req_buf_size));
+	return simple_read_from_buffer(buffer, length, offset, &chardev_priv->req_buf_size,
+				       sizeof(chardev_priv->req_buf_size));
 }
 
 static long dell_smbios_wmi_do_ioctl(struct wmi_smbios_priv *priv,
@@ -159,20 +147,18 @@ static long dell_smbios_wmi_do_ioctl(struct wmi_smbios_priv *priv,
 static long dell_smbios_wmi_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct dell_wmi_smbios_buffer __user *input = (struct dell_wmi_smbios_buffer __user *)arg;
-	struct wmi_smbios_priv *priv;
 
 	if (cmd != DELL_WMI_SMBIOS_CMD)
 		return -ENOIOCTLCMD;
 
-	guard(rwsem_read)(&list_lock);
+	guard(rwsem_read)(&chardev_lock);
 
-	priv = get_first_smbios_priv();
-	if (!priv)
+	if (!chardev_priv)
 		return -ENODEV;
 
-	guard(mutex)(&priv->call_lock);
+	guard(mutex)(&chardev_priv->call_lock);
 
-	return dell_smbios_wmi_do_ioctl(priv, input);
+	return dell_smbios_wmi_do_ioctl(chardev_priv, input);
 }
 
 static const struct file_operations dell_smbios_wmi_fops = {
@@ -189,10 +175,29 @@ static void dell_smbios_wmi_unregister_chardev(void *data)
 	misc_deregister(char_dev);
 }
 
+static void dell_smbios_wmi_clear_chardev(void *data)
+{
+	guard(rwsem_write)(&chardev_lock);
+
+	chardev_priv = NULL;
+}
+
 static int dell_smbios_wmi_register_chardev(struct wmi_smbios_priv *priv)
 {
 	int ret;
 
+	scoped_guard(rwsem_write, &chardev_lock) {
+		/* We can only have a single chardev at a time */
+		if (chardev_priv)
+			return -EBUSY;
+
+		chardev_priv = priv;
+	}
+
+	ret = devm_add_action_or_reset(&priv->wdev->dev, dell_smbios_wmi_clear_chardev, NULL);
+	if (ret < 0)
+		return ret;
+
 	priv->char_dev.minor = MISC_DYNAMIC_MINOR;
 	priv->char_dev.name = "wmi/dell-smbios";
 	priv->char_dev.fops = &dell_smbios_wmi_fops;
@@ -256,24 +261,12 @@ static int dell_smbios_wmi_probe(struct wmi_device *wdev, const void *context)
 	if (ret)
 		return ret;
 
-	ret = dell_smbios_register_device(&wdev->dev, 1, &dell_smbios_wmi_call);
-	if (ret)
-		return ret;
-
-	guard(rwsem_write)(&list_lock);
-	list_add_tail(&priv->list, &wmi_list);
-
-	return 0;
+	return dell_smbios_register_device(&wdev->dev, 1, &dell_smbios_wmi_call);
 }
 
 static void dell_smbios_wmi_remove(struct wmi_device *wdev)
 {
-	struct wmi_smbios_priv *priv = dev_get_drvdata(&wdev->dev);
-
 	dell_smbios_unregister_device(&wdev->dev);
-
-	guard(rwsem_write)(&list_lock);
-	list_del(&priv->list);
 }
 
 static const struct wmi_device_id dell_smbios_wmi_id_table[] = {
@@ -311,6 +304,7 @@ static struct wmi_driver dell_smbios_wmi_driver = {
 	.probe = dell_smbios_wmi_probe,
 	.remove = dell_smbios_wmi_remove,
 	.id_table = dell_smbios_wmi_id_table,
+	.no_singleton = true,
 };
 
 int init_dell_smbios_wmi(void)
-- 
2.39.5