s390/chsc: use notifier for AP configuration changes

The direct dependency of chsc and the AP bus prevents the
modularization of ap bus. Introduce a notifier interface for AP
changes, which decouples the producer of the change events (chsc) from
the consumer (ap_bus).

Remove the ap_cfg_chg() interface and replace it with the notifier
invocation. The ap bus module registers a notification handler, which
triggers the AP bus scan.

Cc: Vineeth Vijayan <[e-mail]>
Cc: Peter Oberparleiter <[e-mail]>
Signed-off-by: Holger Dengler <[e-mail]>
Reviewed-by: Harald Freudenberger <[e-mail]>
Acked-by: Vineeth Vijayan <[e-mail]>
Signed-off-by: Alexander Gordeev <[e-mail]>

arch/s390/include/asm/ap.h

···
 	return reg1.status;
 }
 
-/*
- * Interface to tell the AP bus code that a configuration
- * change has happened. The bus code should at least do
- * an ap bus resource rescan.
- */
-#if IS_ENABLED(CONFIG_ZCRYPT)
-void ap_bus_cfg_chg(void);
-#else
-static inline void ap_bus_cfg_chg(void){}
-#endif
-
 #endif /* _ASM_S390_AP_H_ */

arch/s390/include/asm/chsc.h

···
 
 #include <uapi/asm/chsc.h>
 
+/* struct from linux/notifier.h */
+struct notifier_block;
+
 /**
  * Operation codes for CHSC PNSO:
  *    PNSO_OC_NET_BRIDGE_INFO - only addresses that are visible to a bridgeport
···
 	struct chsc_pnso_naihdr naihdr;
 	struct chsc_pnso_naid_l2 entries[];
 } __packed __aligned(PAGE_SIZE);
+
+/*
+ * notifier interface - registered notifiers gets called on
+ * the following events:
+ * - ap config changed (CHSC_NOTIFY_AP_CFG)
+ */
+enum chsc_notify_type {
+	CHSC_NOTIFY_AP_CFG = 3,
+};
+
+int chsc_notifier_register(struct notifier_block *nb);
+int chsc_notifier_unregister(struct notifier_block *nb);
 
 #endif /* _ASM_S390_CHSC_H */

drivers/s390/cio/chsc.c

···
 #include <asm/crw.h>
 #include <asm/isc.h>
 #include <asm/ebcdic.h>
-#include <asm/ap.h>
 
 #include "css.h"
 #include "cio.h"
···
 
 #define SEI_VF_FLA	0xc0 /* VF flag for Full Link Address */
 #define SEI_RS_CHPID	0x4  /* 4 in RS field indicates CHPID */
+
+static BLOCKING_NOTIFIER_HEAD(chsc_notifiers);
+
+int chsc_notifier_register(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&chsc_notifiers, nb);
+}
+EXPORT_SYMBOL(chsc_notifier_register);
+
+int chsc_notifier_unregister(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&chsc_notifiers, nb);
+}
+EXPORT_SYMBOL(chsc_notifier_unregister);
 
 /**
  * chsc_error_from_response() - convert a chsc response to an error
···
 	if (sei_area->rs != 5)
 		return;
 
-	ap_bus_cfg_chg();
+	blocking_notifier_call_chain(&chsc_notifiers,
+				     CHSC_NOTIFY_AP_CFG, NULL);
 }
 
 static void chsc_process_sei_fces_event(struct chsc_sei_nt0_area *sei_area)

drivers/s390/crypto/ap_bus.c

···
 #include <linux/ctype.h>
 #include <linux/module.h>
 #include <asm/uv.h>
+#include <asm/chsc.h>
 
 #include "ap_bus.h"
 #include "ap_debug.h"
···
 /*
  * A config change has happened, force an ap bus rescan.
  */
-void ap_bus_cfg_chg(void)
+static int ap_bus_cfg_chg(struct notifier_block *nb,
+			  unsigned long action, void *data)
 {
+	if (action != CHSC_NOTIFY_AP_CFG)
+		return NOTIFY_DONE;
+
 	pr_debug("%s config change, forcing bus rescan\n", __func__);
 
 	ap_bus_force_rescan();
+
+	return NOTIFY_OK;
 }
+
+static struct notifier_block ap_bus_nb = {
+	.notifier_call = ap_bus_cfg_chg,
+};
 
 /*
  * hex2bitmap() - parse hex mask string and set bitmap.
···
 
 	queue_work(system_long_wq, &ap_scan_bus_work);
 
+	rc = chsc_notifier_register(&ap_bus_nb);
+	if (rc)
+		goto out;
+
 	/* Start the low priority AP bus poll thread. */
 	if (!ap_thread_flag)
 		return 0;
 
 	rc = ap_poll_thread_start();
 	if (rc)
-		goto out;
+		goto out_notifier;
 
 	return 0;
 
+out_notifier:
+	chsc_notifier_unregister(&ap_bus_nb);
 out:
 	cancel_work(&ap_scan_bus_work);
 	hrtimer_cancel(&ap_poll_timer);