[RFC 1/3] drivers pps: add PPS generators support

Rodolfo Giometti
2024-10-08T13:53:45Z

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>
---
drivers/pps/Makefile | 3 +-
drivers/pps/generators/Kconfig | 19 +-
drivers/pps/generators/Makefile | 4 +
drivers/pps/generators/pps_gen-dummy.c | 83 ++++++++
drivers/pps/generators/pps_gen.c | 283 +++++++++++++++++++++++++
drivers/pps/generators/sysfs.c | 89 ++++++++
include/linux/pps_gen_kernel.h | 57 +++++
include/uapi/linux/pps_gen.h | 35 +++
8 files changed, 571 insertions(+), 2 deletions(-)
create mode 100644 drivers/pps/generators/pps_gen-dummy.c
create mode 100644 drivers/pps/generators/pps_gen.c
create mode 100644 drivers/pps/generators/sysfs.c
create mode 100644 include/linux/pps_gen_kernel.h
create mode 100644 include/uapi/linux/pps_gen.h

diff --git a/drivers/pps/Makefile b/drivers/pps/Makefile
index ceaf65cc1f1d..0aea394d4e4d 100644
--- a/drivers/pps/Makefile
+++ b/drivers/pps/Makefile
@@ -6,6 +6,7 @@
pps_core-y := pps.o kapi.o sysfs.o
pps_core-$(CONFIG_NTP_PPS) += kc.o
obj-$(CONFIG_PPS) := pps_core.o
-obj-y += clients/ generators/
+obj-y += clients/
+obj-$(CONFIG_PPS_GENERATOR) += generators/

ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
diff --git a/drivers/pps/generators/Kconfig b/drivers/pps/generators/Kconfig
index d615e640fcad..e3dfe31609ba 100644
--- a/drivers/pps/generators/Kconfig
+++ b/drivers/pps/generators/Kconfig
@@ -3,7 +3,22 @@
# PPS generators configuration
#

-comment "PPS generators support"
+menuconfig PPS_GENERATOR
+ tristate "PPS generators support"
+ help
+ PPS generators are special hardware which are able to produce PPS
+ (Pulse Per Second) signals.
+
+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 actual 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"
@@ -12,3 +27,5 @@ config PPS_GENERATOR_PARPORT
If you say yes here you get support for a PPS signal generator which
utilizes STROBE pin of a parallel port to send PPS signals. It uses
parport abstraction layer and hrtimers to precisely control the signal.
+
+endif # PPS_GENERATOR
diff --git a/drivers/pps/generators/Makefile b/drivers/pps/generators/Makefile
index 2589fd0f2481..dc1aa5a4688b 100644
--- a/drivers/pps/generators/Makefile
+++ b/drivers/pps/generators/Makefile
@@ -3,6 +3,10 @@
# Makefile for PPS generators.
#

+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
diff --git a/drivers/pps/generators/pps_gen-dummy.c b/drivers/pps/generators/pps_gen-dummy.c
new file mode 100644
index 000000000000..2d257f3f9bf9
--- /dev/null
+++ b/drivers/pps/generators/pps_gen-dummy.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPS dummy generator
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/time.h>
+#include <linux/pps_gen_kernel.h>
+
+/*
+ * Global variables
+ */
+
+static struct pps_gen_device *pps_gen;
+
+/*
+ * 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)
+{
+ /* always enabled */
+ return 0;
+}
+
+/*
+ * The PPS info struct
+ */
+
+static struct pps_gen_source_info pps_gen_dummy_info = {
+ .name = "dummy",
+ .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)
+{
+ dev_info(pps_gen->dev, "dummy PPS generator unregistered\n");
+
+ 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)) {
+ pr_err("cannot register PPS generator\n");
+ return PTR_ERR(pps_gen);
+ }
+
+ dev_info(pps_gen->dev, "dummy PPS generator registered\n");
+
+ return 0;
+}
+
+module_init(pps_gen_dummy_init);
+module_exit(pps_gen_dummy_exit);
+
+MODULE_AUTHOR("Rodolfo Giometti <giometti@enneenne.com>");
+MODULE_DESCRIPTION("LinuxPPS dummy generator");
+MODULE_LICENSE("GPL");
diff --git a/drivers/pps/generators/pps_gen.c b/drivers/pps/generators/pps_gen.c
new file mode 100644
index 000000000000..40b05087b4b4
--- /dev/null
+++ b/drivers/pps/generators/pps_gen.c
@@ -0,0 +1,283 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPS generators core file
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/time.h>
+#include <linux/timex.h>
+#include <linux/uaccess.h>
+#include <linux/idr.h>
+#include <linux/mutex.h>
+#include <linux/cdev.h>
+#include <linux/fs.h>
+#include <linux/pps_gen_kernel.h>
+#include <linux/slab.h>
+
+/*
+ * Local variables
+ */
+
+static int pps_gen_major;
+static struct class *pps_gen_class;
+
+static DEFINE_MUTEX(pps_gen_idr_lock);
+static DEFINE_IDR(pps_gen_idr);
+
+/*
+ * Char device methods
+ */
+
+static long pps_gen_cdev_ioctl(struct file *file,
+ unsigned int cmd, unsigned long arg)
+{
+ struct pps_gen_device *pps_gen = file->private_data;
+ unsigned int __user *uiuarg = (unsigned int __user *) arg;
+ unsigned int status;
+ int ret;
+
+ switch (cmd) {
+ case PPS_GEN_SETENABLE:
+ dev_dbg(pps_gen->dev, "PPS_GEN_SETENABLE\n");
+
+ ret = get_user(status, uiuarg);
+ if (ret)
+ return -EFAULT;
+
+ ret = pps_gen->info.enable(pps_gen, status);
+ if (ret)
+ return ret;
+ pps_gen->enabled = status;
+
+ break;
+
+ default:
+ return -ENOTTY;
+ }
+
+ return 0;
+}
+
+#ifdef CONFIG_COMPAT
+static long pps_gen_cdev_compat_ioctl(struct file *file,
+ unsigned int cmd, unsigned long arg)
+{
+ cmd = _IOC(_IOC_DIR(cmd), _IOC_TYPE(cmd), _IOC_NR(cmd), sizeof(void *));
+ return pps_gen_cdev_ioctl(file, cmd, arg);
+}
+#else
+#define pps_gen_cdev_compat_ioctl NULL
+#endif
+
+static struct pps_gen_device *pps_gen_idr_get(unsigned long id)
+{
+ struct pps_gen_device *pps_gen;
+
+ mutex_lock(&pps_gen_idr_lock);
+ pps_gen = idr_find(&pps_gen_idr, id);
+ if (pps_gen)
+ kobject_get(&pps_gen->dev->kobj);
+
+ mutex_unlock(&pps_gen_idr_lock);
+ return pps_gen;
+}
+
+static int pps_gen_cdev_open(struct inode *inode, struct file *file)
+{
+ struct pps_gen_device *pps_gen = pps_gen_idr_get(iminor(inode));
+
+ if (!pps_gen)
+ return -ENODEV;
+
+ file->private_data = pps_gen;
+ return 0;
+}
+
+static int pps_gen_cdev_release(struct inode *inode, struct file *file)
+{
+ struct pps_gen_device *pps_gen = file->private_data;
+
+ WARN_ON(pps_gen->id != iminor(inode));
+ kobject_put(&pps_gen->dev->kobj);
+ return 0;
+}
+
+/*
+ * Char device stuff
+ */
+
+static const struct file_operations pps_gen_cdev_fops = {
+ .owner = THIS_MODULE,
+ .compat_ioctl = pps_gen_cdev_compat_ioctl,
+ .unlocked_ioctl = pps_gen_cdev_ioctl,
+ .open = pps_gen_cdev_open,
+ .release = pps_gen_cdev_release,
+};
+
+static void pps_gen_device_destruct(struct device *dev)
+{
+ struct pps_gen_device *pps_gen = dev_get_drvdata(dev);
+
+ pr_debug("deallocating pps-gen%d\n", pps_gen->id);
+ kfree(dev);
+ kfree(pps_gen);
+}
+
+static int pps_gen_register_cdev(struct pps_gen_device *pps_gen)
+{
+ int err;
+ dev_t devt;
+
+ mutex_lock(&pps_gen_idr_lock);
+
+ err = idr_alloc(&pps_gen_idr, pps_gen, 0, PPS_GEN_MAX_SOURCES,
+ GFP_KERNEL);
+ if (err < 0) {
+ if (err == -ENOSPC) {
+ pr_err("%s: too many PPS sources in the system\n",
+ pps_gen->info.name);
+ err = -EBUSY;
+ }
+ goto out_unlock;
+ }
+ pps_gen->id = err;
+
+ devt = MKDEV(pps_gen_major, pps_gen->id);
+ pps_gen->dev = device_create(pps_gen_class, pps_gen->info.parent, devt,
+ pps_gen, "pps-gen%d", pps_gen->id);
+ if (IS_ERR(pps_gen->dev)) {
+ err = PTR_ERR(pps_gen->dev);
+ goto free_idr;
+ }
+
+ /* Override the release function with our own */
+ pps_gen->dev->release = pps_gen_device_destruct;
+
+ pr_debug("generator %s got cdev (%d:%d)\n",
+ pps_gen->info.name, pps_gen_major, pps_gen->id);
+
+ kobject_get(&pps_gen->dev->kobj);
+ mutex_unlock(&pps_gen_idr_lock);
+ return 0;
+
+free_idr:
+ idr_remove(&pps_gen_idr, pps_gen->id);
+out_unlock:
+ mutex_unlock(&pps_gen_idr_lock);
+ return err;
+}
+
+static void pps_gen_unregister_cdev(struct pps_gen_device *pps_gen)
+{
+ pr_debug("unregistering pps-gen%d\n", pps_gen->id);
+ device_destroy(pps_gen_class, pps_gen->dev->devt);
+
+ /* Now we can release the ID for re-use */
+ mutex_lock(&pps_gen_idr_lock);
+ idr_remove(&pps_gen_idr, pps_gen->id);
+ kobject_put(&pps_gen->dev->kobj);
+ mutex_unlock(&pps_gen_idr_lock);
+}
+
+/*
+ * Exported functions
+ */
+
+/* pps_gen_register_source - add a PPS generator in the system
+ * @info: the PPS generator info struct
+ *
+ * The function returns, in case of success, the PPS generaor device. Otherwise
+ * ERR_PTR(errno).
+ */
+
+struct pps_gen_device *pps_gen_register_source(struct pps_gen_source_info *info)
+{
+ struct pps_gen_device *pps_gen;
+ int err;
+
+ pps_gen = kzalloc(sizeof(struct pps_gen_device), GFP_KERNEL);
+ if (pps_gen == NULL) {
+ err = -ENOMEM;
+ goto pps_gen_register_source_exit;
+ }
+ pps_gen->info = *info;
+ pps_gen->enabled = false;
+
+ /* Create the char device */
+ err = pps_gen_register_cdev(pps_gen);
+ if (err < 0) {
+ pr_err("%s: unable to create char device\n",
+ info->name);
+ goto kfree_pps_gen;
+ }
+
+ dev_info(pps_gen->dev, "new PPS generator %s\n", info->name);
+
+ return pps_gen;
+
+kfree_pps_gen:
+ kfree(pps_gen);
+
+pps_gen_register_source_exit:
+ pr_err("%s: unable to register generaor\n", info->name);
+
+ return ERR_PTR(err);
+}
+EXPORT_SYMBOL(pps_gen_register_source);
+
+/* pps_gen_unregister_source - remove a PPS generator from the system
+ * @pps_gen: the PPS generator
+ */
+
+void pps_gen_unregister_source(struct pps_gen_device *pps_gen)
+{
+ pps_gen_unregister_cdev(pps_gen);
+}
+EXPORT_SYMBOL(pps_gen_unregister_source);
+
+/*
+ * Module stuff
+ */
+
+static void __exit pps_gen_exit(void)
+{
+ class_destroy(pps_gen_class);
+ __unregister_chrdev(pps_gen_major, 0, PPS_GEN_MAX_SOURCES, "pps-gen");
+}
+
+static int __init pps_gen_init(void)
+{
+ pps_gen_class = class_create("pps-gen");
+ if (IS_ERR(pps_gen_class)) {
+ pr_err("failed to allocate class\n");
+ return PTR_ERR(pps_gen_class);
+ }
+ pps_gen_class->dev_groups = pps_gen_groups;
+
+ pps_gen_major = __register_chrdev(0, 0, PPS_GEN_MAX_SOURCES, "pps-gen",
+ &pps_gen_cdev_fops);
+ if (pps_gen_major < 0) {
+ pr_err("failed to allocate char device region\n");
+ goto remove_class;
+ }
+
+ return 0;
+
+remove_class:
+ class_destroy(pps_gen_class);
+ return pps_gen_major;
+}
+
+subsys_initcall(pps_gen_init);
+module_exit(pps_gen_exit);
+
+MODULE_AUTHOR("Rodolfo Giometti <giometti@enneenne.com>");
+MODULE_DESCRIPTION("LinuxPPS generators support");
+MODULE_LICENSE("GPL");
diff --git a/drivers/pps/generators/sysfs.c b/drivers/pps/generators/sysfs.c
new file mode 100644
index 000000000000..247030d138e1
--- /dev/null
+++ b/drivers/pps/generators/sysfs.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * PPS generators sysfs support
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/pps_gen_kernel.h>
+
+/*
+ * Attribute functions
+ */
+
+static ssize_t system_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct pps_gen_device *pps_gen = dev_get_drvdata(dev);
+
+ return sysfs_emit(buf, "%d\n", pps_gen->info.use_system_clock);
+}
+static DEVICE_ATTR_RO(system);
+
+static ssize_t time_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct pps_gen_device *pps_gen = dev_get_drvdata(dev);
+ struct timespec64 time;
+ int ret;
+
+ ret = pps_gen->info.get_time(pps_gen, &time);
+ if (ret)
+ return ret;
+
+ return sysfs_emit(buf, "%llu %09lu\n", time.tv_sec, time.tv_nsec);
+}
+static DEVICE_ATTR_RO(time);
+
+static ssize_t enable_store(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct pps_gen_device *pps_gen = dev_get_drvdata(dev);
+ bool status;
+ unsigned int enable;
+ int ret;
+
+ ret = sscanf(buf, "%u", &enable);
+ if (ret != 1)
+ return -EINVAL;
+ status = !!enable;
+
+ ret = pps_gen->info.enable(pps_gen, status);
+ if (ret)
+ return ret;
+ pps_gen->enabled = status;
+
+ return count;
+}
+static DEVICE_ATTR_WO(enable);
+
+static ssize_t name_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct pps_gen_device *pps_gen = dev_get_drvdata(dev);
+
+ return sysfs_emit(buf, "%s\n", pps_gen->info.name);
+}
+static DEVICE_ATTR_RO(name);
+
+static struct attribute *pps_gen_attrs[] = {
+ &dev_attr_enable.attr,
+ &dev_attr_name.attr,
+ &dev_attr_time.attr,
+ &dev_attr_system.attr,
+ NULL,
+};
+
+static const struct attribute_group pps_gen_group = {
+ .attrs = pps_gen_attrs,
+};
+
+const struct attribute_group *pps_gen_groups[] = {
+ &pps_gen_group,
+ NULL,
+};
diff --git a/include/linux/pps_gen_kernel.h b/include/linux/pps_gen_kernel.h
new file mode 100644
index 000000000000..5513415b53ec
--- /dev/null
+++ b/include/linux/pps_gen_kernel.h
@@ -0,0 +1,57 @@
+/* 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
+ */
+
+struct pps_gen_device;
+
+/* The specific PPS source info */
+struct pps_gen_source_info {
+ char name[PPS_GEN_MAX_NAME_LEN]; /* symbolic name */
+ 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);
+
+ 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 id; /* PPS generator unique ID */
+ struct device *dev;
+};
+
+/*
+ * 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);
+
+#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..7b6f50fcab8c
--- /dev/null
+++ b/include/uapi/linux/pps_gen.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * PPS generator API header
+ *
+ * Copyright (C) 2024 Rodolfo Giometti <giometti@enneenne.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+
+#ifndef _PPS_GEN_H_
+#define _PPS_GEN_H_
+
+#include <linux/types.h>
+
+#define PPS_GEN_MAX_SOURCES 16 /* should be enough... */
+#define PPS_GEN_MAX_NAME_LEN 32
+
+#include <linux/ioctl.h>
+
+#define PPS_GEN_SETENABLE _IOW('g', 0xa1, unsigned int *)
+
+#endif /* _PPS_GEN_H_ */
--
2.34.1