Export some rather helpful read/write WMI symbols using a namespace.
These are DEVS and DSTS only, or require the arg0 input.

Also does a slight refactor of internals of these functions.

Signed-off-by: Luke D. Jones <luke@ljones.dev>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/platform/x86/asus-wmi.c            | 51 ++++++++++++++++++++--
 include/linux/platform_data/x86/asus-wmi.h | 10 +++++
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 6725a27df62f..0a5221d65130 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -385,7 +385,7 @@ int asus_wmi_evaluate_method(u32 method_id, u32 arg0, u32 arg1, u32 *retval)
 {
 	return asus_wmi_evaluate_method3(method_id, arg0, arg1, 0, retval);
 }
-EXPORT_SYMBOL_GPL(asus_wmi_evaluate_method);
+EXPORT_SYMBOL_NS_GPL(asus_wmi_evaluate_method, ASUS_WMI);
 
 static int asus_wmi_evaluate_method5(u32 method_id,
 		u32 arg0, u32 arg1, u32 arg2, u32 arg3, u32 arg4, u32 *retval)
@@ -549,12 +549,57 @@ static int asus_wmi_get_devstate(struct asus_wmi *asus, u32 dev_id, u32 *retval)
 	return 0;
 }
 
-static int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param,
-				 u32 *retval)
+/**
+ * asus_wmi_get_devstate_dsts() - Get the WMI function state.
+ * @dev_id: The WMI function to call.
+ * @retval: A pointer to where to store the value returned from WMI.
+ *
+ * The returned WMI function state can also be used to determine if the WMI
+ * function is supported by checking if the asus_wmi_get_devstate_dsts()
+ * returns an error.
+ *
+ * On success the return value is 0, and the retval is a valid value returned
+ * by the successful WMI function call. An error value is returned only if the
+ * WMI function failed, or if it returns "unsupported" which is typically a 0
+ * (no return, and no 'supported' bit set), or a 0xFFFFFFFE (~1) which if not
+ * caught here can result in unexpected behaviour later.
+ */
+int asus_wmi_get_devstate_dsts(u32 dev_id, u32 *retval)
+{
+	int err;
+
+	err = asus_wmi_evaluate_method(ASUS_WMI_METHODID_DSTS, dev_id, 0, retval);
+	if (err)
+		return err;
+
+	*retval &= ~ASUS_WMI_DSTS_PRESENCE_BIT;
+	if (*retval == ASUS_WMI_UNSUPPORTED_METHOD)
+		return -ENODEV;
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(asus_wmi_get_devstate_dsts, ASUS_WMI);
+
+/**
+ * asus_wmi_set_devstate() - Set the WMI function state.
+ * @dev_id: The WMI function to call.
+ * @ctrl_param: The argument to be used for this WMI function.
+ * @retval: A pointer to where to store the value returned from WMI.
+ *
+ * The returned WMI function state if not checked here for error as
+ * asus_wmi_set_devstate() is not called unless first paired with a call to
+ * asus_wmi_get_devstate_dsts() to check that the WMI function is supported.
+ *
+ * On success the return value is 0, and the retval is a valid value returned
+ * by the successful WMI function call. An error value is returned only if the
+ * WMI function failed.
+ */
+int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param, u32 *retval)
 {
 	return asus_wmi_evaluate_method(ASUS_WMI_METHODID_DEVS, dev_id,
 					ctrl_param, retval);
 }
+EXPORT_SYMBOL_NS_GPL(asus_wmi_set_devstate, ASUS_WMI);
 
 /* Helper for special devices with magic return codes */
 static int asus_wmi_get_devstate_bits(struct asus_wmi *asus,
diff --git a/include/linux/platform_data/x86/asus-wmi.h b/include/linux/platform_data/x86/asus-wmi.h
index 365e119bebaa..6ea4dedfb85e 100644
--- a/include/linux/platform_data/x86/asus-wmi.h
+++ b/include/linux/platform_data/x86/asus-wmi.h
@@ -158,8 +158,18 @@
 #define ASUS_WMI_DSTS_LIGHTBAR_MASK	0x0000000F
 
 #if IS_REACHABLE(CONFIG_ASUS_WMI)
+int asus_wmi_get_devstate_dsts(u32 dev_id, u32 *retval);
+int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param, u32 *retval);
 int asus_wmi_evaluate_method(u32 method_id, u32 arg0, u32 arg1, u32 *retval);
 #else
+static inline int asus_wmi_get_devstate_dsts(u32 dev_id, u32 *retval)
+{
+	return -ENODEV;
+}
+static inline int asus_wmi_set_devstate(u32 dev_id, u32 ctrl_param, u32 *retval)
+{
+	return -ENODEV;
+}
 static inline int asus_wmi_evaluate_method(u32 method_id, u32 arg0, u32 arg1,
 					   u32 *retval)
 {
-- 
2.46.1