gnss: add GNSS receiver subsystem

Add a new subsystem for GNSS (e.g. GPS) receivers.

While GNSS receivers are typically accessed using a UART interface they
often also support other I/O interfaces such as I2C, SPI and USB, while
yet other devices use iomem or even some form of remote-processor
messaging (rpmsg).

The new GNSS subsystem abstracts the underlying interface and provides a
new "gnss" class type, which exposes a character-device interface (e.g.
/dev/gnss0) to user space. This allows GNSS receivers to have a
representation in the Linux device model, something which is important
not least for power management purposes.

Note that the character-device interface provides raw access to whatever
protocol the receiver is (currently) using, such as NMEA 0183, UBX or
SiRF Binary. These protocols are expected to be continued to be handled
by user space for the time being, even if some hybrid solutions are also
conceivable (e.g. to have kernel drivers issue management commands).

This will still allow for better platform integration by allowing GNSS
devices and their resources (e.g. regulators and enable-gpios) to be
described by firmware and managed by kernel drivers rather than
platform-specific scripts and services.

While the current interface is kept minimal, it could be extended using
IOCTLs, sysfs or uevents as needs and proper abstraction levels are
identified and determined (e.g. for device and feature identification).

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 66 insertions, 0 deletions

diff --git a/include/linux/gnss.h b/include/linux/gnss.h
new file mode 100644
index 000000000000..e26aeac1e0e2
--- /dev/null
+++ b/include/linux/gnss.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * GNSS receiver support
+ *
+ * Copyright (C) 2018 Johan Hovold <johan@kernel.org>
+ */
+
+#ifndef _LINUX_GNSS_H
+#define _LINUX_GNSS_H
+
+#include <linux/cdev.h>
+#include <linux/device.h>
+#include <linux/kfifo.h>
+#include <linux/mutex.h>
+#include <linux/rwsem.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+
+struct gnss_device;
+
+struct gnss_operations {
+	int (*open)(struct gnss_device *gdev);
+	void (*close)(struct gnss_device *gdev);
+	int (*write_raw)(struct gnss_device *gdev, const unsigned char *buf,
+				size_t count);
+};
+
+struct gnss_device {
+	struct device dev;
+	struct cdev cdev;
+	int id;
+
+	unsigned long flags;
+
+	struct rw_semaphore rwsem;
+	const struct gnss_operations *ops;
+	unsigned int count;
+	unsigned int disconnected:1;
+
+	struct mutex read_mutex;
+	struct kfifo read_fifo;
+	wait_queue_head_t read_queue;
+
+	struct mutex write_mutex;
+	char *write_buf;
+};
+
+struct gnss_device *gnss_allocate_device(struct device *parent);
+void gnss_put_device(struct gnss_device *gdev);
+int gnss_register_device(struct gnss_device *gdev);
+void gnss_deregister_device(struct gnss_device *gdev);
+
+int gnss_insert_raw(struct gnss_device *gdev, const unsigned char *buf,
+			size_t count);
+
+static inline void gnss_set_drvdata(struct gnss_device *gdev, void *data)
+{
+	dev_set_drvdata(&gdev->dev, data);
+}
+
+static inline void *gnss_get_drvdata(struct gnss_device *gdev)
+{
+	return dev_get_drvdata(&gdev->dev);
+}
+
+#endif /* _LINUX_GNSS_H */