drivers pps: add PPS generators support

Sometimes one needs to be able not only to catch PPS signals but to
produce them also. For example, running a distributed simulation,
which requires computers' clock to be synchronized very tightly.

This patch adds PPS generators class in order to have a well-defined
interface for these devices.

Signed-off-by: Rodolfo Giometti <giometti@enneenne.com>
Link: https://lore.kernel.org/r/20241108073115.759039-2-giometti@enneenne.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 115 insertions, 0 deletions

diff --git a/include/linux/pps_gen_kernel.h b/include/linux/pps_gen_kernel.h
new file mode 100644
index 000000000000..022ea0ac4440
--- /dev/null
+++ b/include/linux/pps_gen_kernel.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * PPS generator API kernel header
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ */
+
+#ifndef LINUX_PPS_GEN_KERNEL_H
+#define LINUX_PPS_GEN_KERNEL_H
+
+#include <linux/pps_gen.h>
+#include <linux/cdev.h>
+#include <linux/device.h>
+
+/*
+ * Global defines
+ */
+
+#define PPS_GEN_MAX_SOURCES	16		/* should be enough... */
+
+struct pps_gen_device;
+
+/**
+ * struct pps_gen_source_info - the specific PPS generator info
+ * @use_system_clock: true, if the system clock is used to generate pulses
+ * @get_time: query the time stored into the generator clock
+ * @enable: enable/disable the PPS pulses generation
+ *
+ * This is the main generator struct where all needed information must be
+ * placed before calling the pps_gen_register_source().
+ */
+struct pps_gen_source_info {
+	bool use_system_clock;
+
+	int (*get_time)(struct pps_gen_device *pps_gen,
+					struct timespec64 *time);
+	int (*enable)(struct pps_gen_device *pps_gen, bool enable);
+
+/* private: internal use only */
+	struct module *owner;
+	struct device *parent;			/* for device_create */
+};
+
+/* The main struct */
+struct pps_gen_device {
+	struct pps_gen_source_info info;	/* PSS generator info */
+	bool enabled;				/* PSS generator status */
+
+	unsigned int event;
+	unsigned int sequence;
+
+	unsigned int last_ev;			/* last PPS event id */
+	wait_queue_head_t queue;		/* PPS event queue */
+
+	unsigned int id;			/* PPS generator unique ID */
+	struct cdev cdev;
+	struct device *dev;
+	struct fasync_struct *async_queue;	/* fasync method */
+	spinlock_t lock;
+};
+
+/*
+ * Global variables
+ */
+
+extern const struct attribute_group *pps_gen_groups[];
+
+/*
+ * Exported functions
+ */
+
+extern struct pps_gen_device *pps_gen_register_source(
+				struct pps_gen_source_info *info);
+extern void pps_gen_unregister_source(struct pps_gen_device *pps_gen);
+extern void pps_gen_event(struct pps_gen_device *pps_gen,
+				unsigned int event, void *data);
+
+#endif /* LINUX_PPS_GEN_KERNEL_H */
diff --git a/include/uapi/linux/pps_gen.h b/include/uapi/linux/pps_gen.h
new file mode 100644
index 000000000000..60a5d0fcfa68
--- /dev/null
+++ b/include/uapi/linux/pps_gen.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * PPS generator API header
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ */
+
+#ifndef _PPS_GEN_H_
+#define _PPS_GEN_H_
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+/**
+ * struct pps_gen_event - the PPS generator events
+ * @event: the event type
+ * @sequence: the event sequence number
+ *
+ * Userspace can get the last PPS generator event by using the
+ * ioctl(pps_gen, PPS_GEN_FETCHEVENT, ...) syscall.
+ * The sequence field can be used to save the last event ID, while in the
+ * event field is stored the last event type. Currently known event is:
+ *
+ *     PPS_GEN_EVENT_MISSEDPULSE	: last pulse was not generated
+ */
+struct pps_gen_event {
+	unsigned int event;
+	unsigned int sequence;
+};
+
+#define PPS_GEN_EVENT_MISSEDPULSE	1
+
+#define PPS_GEN_SETENABLE		_IOW('p', 0xb1, unsigned int *)
+#define PPS_GEN_USESYSTEMCLOCK		_IOR('p', 0xb2, unsigned int *)
+#define PPS_GEN_FETCHEVENT		_IOR('p', 0xb3, struct pps_gen_event *)
+
+#endif /* _PPS_GEN_H_ */