um: Implement ndelay/udelay in time-travel mode

In external or inf-cpu time-travel mode, ndelay/udelay currently
just waste CPU time since the simulation time doesn't advance.
Implement them properly in this case.

Note that the "if (time_travel_mode == ...)" parts compile out
if CONFIG_UML_TIME_TRAVEL_SUPPORT isn't set, time_travel_mode is
defined to TT_MODE_OFF in that case.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/Kbuild

@@ -3,7 +3,6 @@ generic-y += bpf_perf_event.h
 generic-y += bug.h
 generic-y += compat.h
 generic-y += current.h
-generic-y += delay.h
 generic-y += device.h
 generic-y += emergency-restart.h
 generic-y += exec.h

arch/um/include/asm/delay.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_DELAY_H
+#define __UM_DELAY_H
+#include <asm-generic/delay.h>
+#include <linux/time-internal.h>
+
+static inline void um_ndelay(unsigned long nsecs)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL) {
+		time_travel_ndelay(nsecs);
+		return;
+	}
+	ndelay(nsecs);
+}
+#undef ndelay
+#define ndelay um_ndelay
+
+static inline void um_udelay(unsigned long usecs)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL) {
+		time_travel_ndelay(1000 * usecs);
+		return;
+	}
+	udelay(usecs);
+}
+#undef udelay
+#define udelay um_udelay
+#endif /* __UM_DELAY_H */

arch/um/include/linux/time-internal.h

@@ -75,4 +75,10 @@ static inline void time_travel_wait_readable(int fd)
 {
 }
 #endif /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
+
+/*
+ * Without CONFIG_UML_TIME_TRAVEL_SUPPORT this is a linker error if used,
+ * which is intentional since we really shouldn't link it in that case.
+ */
+void time_travel_ndelay(unsigned long nsec);
 #endif /* __TIMER_INTERNAL_H__ */

arch/um/kernel/time.c

@@ -374,6 +374,12 @@ static void time_travel_update_time(unsigned long long next, bool idle)
 	time_travel_del_event(&ne);
 }
 
+void time_travel_ndelay(unsigned long nsec)
+{
+	time_travel_update_time(time_travel_time + nsec, false);
+}
+EXPORT_SYMBOL(time_travel_ndelay);
+
 void time_travel_add_irq_event(struct time_travel_event *e)
 {
 	BUG_ON(time_travel_mode != TT_MODE_EXTERNAL);