drivers pps/generators: add dummy PPS generator

This dummy PPS generator can be used for debugging and documentation
purposes.

Signed-off-by: Rodolfo Giometti <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/pps/generators/Kconfig

···
 
 if PPS_GENERATOR
 
+config PPS_GENERATOR_DUMMY
+        tristate "Dummy PPS generator (Testing generator, use for debug)"
+        help
+          If you say yes here you get support for a PPS debugging generator
+          (which generates no PPS signal at all).
+
+          This driver can also be built as a module.  If so, the module
+          will be called pps_gen-dummy.
+
 config PPS_GENERATOR_PARPORT
 	tristate "Parallel port PPS signal generator"
 	depends on PARPORT && BROKEN

drivers/pps/generators/Makefile

···
 pps_gen_core-y			:= pps_gen.o sysfs.o
 obj-$(CONFIG_PPS_GENERATOR)	:= pps_gen_core.o
 
+obj-$(CONFIG_PPS_GENERATOR_DUMMY)   += pps_gen-dummy.o
 obj-$(CONFIG_PPS_GENERATOR_PARPORT) += pps_gen_parport.o
 
 ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG

drivers/pps/generators/pps_gen-dummy.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPS dummy generator
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <[e-mail]>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/time.h>
+#include <linux/timer.h>
+#include <linux/random.h>
+#include <linux/pps_gen_kernel.h>
+
+static struct pps_gen_device *pps_gen;
+static struct timer_list ktimer;
+
+static unsigned int get_random_delay(void)
+{
+	unsigned int delay = get_random_u8() & 0x0f;
+
+	return (delay + 1) * HZ;
+}
+
+/*
+ * The kernel timer
+ */
+
+static void pps_gen_ktimer_event(struct timer_list *unused)
+{
+	pps_gen_event(pps_gen, PPS_GEN_EVENT_MISSEDPULSE, NULL);
+}
+
+/*
+ * PPS Generator methods
+ */
+
+static int pps_gen_dummy_get_time(struct pps_gen_device *pps_gen,
+					struct timespec64 *time)
+{
+	struct system_time_snapshot snap;
+
+	ktime_get_snapshot(&snap);
+	*time = ktime_to_timespec64(snap.real);
+
+	return 0;
+}
+
+static int pps_gen_dummy_enable(struct pps_gen_device *pps_gen, bool enable)
+{
+	if (enable)
+		mod_timer(&ktimer, jiffies + get_random_delay());
+	else
+		del_timer_sync(&ktimer);
+
+	return 0;
+}
+
+/*
+ * The PPS info struct
+ */
+
+static struct pps_gen_source_info pps_gen_dummy_info = {
+	.use_system_clock	= true,
+	.get_time		= pps_gen_dummy_get_time,
+	.enable			= pps_gen_dummy_enable,
+};
+
+/*
+ * Module staff
+ */
+
+static void __exit pps_gen_dummy_exit(void)
+{
+	del_timer_sync(&ktimer);
+	pps_gen_unregister_source(pps_gen);
+}
+
+static int __init pps_gen_dummy_init(void)
+{
+	pps_gen = pps_gen_register_source(&pps_gen_dummy_info);
+	if (IS_ERR(pps_gen))
+		return PTR_ERR(pps_gen);
+
+	timer_setup(&ktimer, pps_gen_ktimer_event, 0);
+
+	return 0;
+}
+
+module_init(pps_gen_dummy_init);
+module_exit(pps_gen_dummy_exit);
+
+MODULE_AUTHOR("Rodolfo Giometti <[e-mail]>");
+MODULE_DESCRIPTION("LinuxPPS dummy generator");
+MODULE_LICENSE("GPL");