x86/platform/intel/iosf_mbi: Add unlocked PMIC bus access notifier unregister

For race free unregistration drivers may need to acquire PMIC bus access
through iosf_mbi_punit_acquire() and then (un)register the notifier without
dropping the lock.

This commit adds an unlocked variant of
iosf_mbi_unregister_pmic_bus_access_notifier for this use case.
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171019111620.26761-2-hdegoede@redhat.com

arch/x86/include/asm/iosf_mbi.h

@@ -145,6 +145,18 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb);
  */
 int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb);
 
+/**
+ * iosf_mbi_unregister_pmic_bus_access_notifier_unlocked - Unregister PMIC bus
+ *                                                         notifier, unlocked
+ *
+ * Like iosf_mbi_unregister_pmic_bus_access_notifier(), but for use when the
+ * caller has already called iosf_mbi_punit_acquire() itself.
+ *
+ * @nb: notifier_block to unregister
+ */
+int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
+	struct notifier_block *nb);
+
 /**
  * iosf_mbi_call_pmic_bus_access_notifier_chain - Call PMIC bus notifier chain
  *
@@ -153,6 +165,11 @@ int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb);
  */
 int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v);
 
+/**
+ * iosf_mbi_assert_punit_acquired - Assert that the P-Unit has been acquired.
+ */
+void iosf_mbi_assert_punit_acquired(void);
+
 #else /* CONFIG_IOSF_MBI is not enabled */
 static inline
 bool iosf_mbi_available(void)
@@ -196,12 +213,20 @@ int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
 	return 0;
 }
 
+static inline int
+iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(struct notifier_block *nb)
+{
+	return 0;
+}
+
 static inline
 int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v)
 {
 	return 0;
 }
 
+static inline void iosf_mbi_assert_punit_acquired(void) {}
+
 #endif /* CONFIG_IOSF_MBI */
 
 #endif /* IOSF_MBI_SYMS_H */

arch/x86/platform/intel/iosf_mbi.c

@@ -218,14 +218,23 @@ int iosf_mbi_register_pmic_bus_access_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(iosf_mbi_register_pmic_bus_access_notifier);
 
+int iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(
+	struct notifier_block *nb)
+{
+	iosf_mbi_assert_punit_acquired();
+
+	return blocking_notifier_chain_unregister(
+				&iosf_mbi_pmic_bus_access_notifier, nb);
+}
+EXPORT_SYMBOL(iosf_mbi_unregister_pmic_bus_access_notifier_unlocked);
+
 int iosf_mbi_unregister_pmic_bus_access_notifier(struct notifier_block *nb)
 {
 	int ret;
 
 	/* Wait for the bus to go inactive before unregistering */
 	mutex_lock(&iosf_mbi_punit_mutex);
-	ret = blocking_notifier_chain_unregister(
-				&iosf_mbi_pmic_bus_access_notifier, nb);
+	ret = iosf_mbi_unregister_pmic_bus_access_notifier_unlocked(nb);
 	mutex_unlock(&iosf_mbi_punit_mutex);
 
 	return ret;
@@ -239,6 +248,12 @@ int iosf_mbi_call_pmic_bus_access_notifier_chain(unsigned long val, void *v)
 }
 EXPORT_SYMBOL(iosf_mbi_call_pmic_bus_access_notifier_chain);
 
+void iosf_mbi_assert_punit_acquired(void)
+{
+	WARN_ON(!mutex_is_locked(&iosf_mbi_punit_mutex));
+}
+EXPORT_SYMBOL(iosf_mbi_assert_punit_acquired);
+
 #ifdef CONFIG_IOSF_MBI_DEBUG
 static u32	dbg_mdr;
 static u32	dbg_mcr;