ANDROID: gnss: Add command line test driver

This driver enables the "takeover" of a serdev bus device by the GNSS
subsystem. It can be used to test the GNSS subsystem without needing to
write a specific hardware backend.

The new module supports the following parameters:

  gnss_cmdline.serdev=driver/port/serdev
  gnss_cmdline.type=<protocol number>

An example which allows GNSS to wrap a platform serial8250 port and
advertise NMEA-0183 data is:

  gnss_cmdline.serdev=serial8250/serial0/serial0-0
                        ^          ^       ^
                       driver     port    serdev
  gnss_cmdline.type=0
                    ^
                    GNSS_TYPE_NMEA

Bug: 146517987
Change-Id: I421386ee4f2ba8f1f0832d9c56a067a600892d3c
Signed-off-by: Alistair Delva <adelva@google.com>

drivers/gnss/Kconfig

@@ -15,4 +15,19 @@ if GNSS
 config GNSS_SERIAL
 	tristate
 
+config GNSS_CMDLINE_SERIAL
+	tristate "Command line test driver for GNSS"
+	depends on SERIAL_DEV_BUS
+	select GNSS_SERIAL
+	---help---
+	  Say Y here if you want to test the GNSS subsystem but do not have a
+	  way to communicate a binding through firmware such as DT or ACPI.
+	  The correct serdev device and protocol type must be specified on
+	  the module command line.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called gnss-cmdline.
+
+	  If unsure, say N.
+
 endif # GNSS

drivers/gnss/Makefile

@@ -8,3 +8,6 @@ gnss-y := core.o
 
 obj-$(CONFIG_GNSS_SERIAL)		+= gnss-serial.o
 gnss-serial-y := serial.o
+
+obj-$(CONFIG_GNSS_CMDLINE_SERIAL)	+= gnss-cmdline.o
+gnss-cmdline-y := cmdline.o

drivers/gnss/cmdline.c

@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test driver for GNSS. This driver requires the serdev binding and protocol
+ * type to be specified on the module command line.
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include <linux/device.h>
+#include <linux/gnss.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/serdev.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include "serial.h"
+
+#define GNSS_CMDLINE_MODULE_NAME "gnss-cmdline"
+
+#define gnss_cmdline_err(...) \
+	pr_err(GNSS_CMDLINE_MODULE_NAME ": " __VA_ARGS__)
+
+static char *serdev;
+module_param(serdev, charp, 0644);
+MODULE_PARM_DESC(serdev, "serial device to wrap");
+
+static int type;
+module_param(type, int, 0644);
+MODULE_PARM_DESC(serdev, "GNSS protocol type (see 'enum gnss_type')");
+
+static struct serdev_device *serdev_device;
+
+static int name_match(struct device *dev, void *data)
+{
+	return strstr(dev_name(dev), data) != NULL;
+}
+
+static int __init gnss_cmdline_init(void)
+{
+	struct device *serial_dev, *port_dev, *serdev_dev;
+	char *driver_name, *port_name, *serdev_name;
+	char *serdev_dup, *serdev_dup_sep;
+	struct gnss_serial *gserial;
+	int err = -ENODEV;
+
+	/* User did not set the serdev module parameter */
+	if (!serdev)
+		return 0;
+
+	if (type < 0 || type >= GNSS_TYPE_COUNT) {
+		gnss_cmdline_err("invalid gnss type '%d'\n", type);
+		return -EINVAL;
+	}
+
+	serdev_dup = serdev_dup_sep = kstrdup(serdev, GFP_KERNEL);
+	if (!serdev_dup)
+		return -ENOMEM;
+
+	driver_name = strsep(&serdev_dup_sep, "/");
+	if (!driver_name) {
+		gnss_cmdline_err("driver name missing\n");
+		goto err_free_serdev_dup;
+	}
+
+	port_name = strsep(&serdev_dup_sep, "/");
+	if (!port_name) {
+		gnss_cmdline_err("port name missing\n");
+		goto err_free_serdev_dup;
+	}
+
+	serdev_name = strsep(&serdev_dup_sep, "/");
+	if (!serdev_name) {
+		gnss_cmdline_err("serdev name missing\n");
+		goto err_free_serdev_dup;
+	}
+
+	/* Find the driver device instance (e.g. serial8250) */
+	serial_dev = bus_find_device_by_name(&platform_bus_type,
+					     NULL, driver_name);
+	if (!serial_dev) {
+		gnss_cmdline_err("no device '%s'\n", driver_name);
+		goto err_free_serdev_dup;
+	}
+
+	/* Find the port device instance (e.g. serial0) */
+	port_dev = device_find_child(serial_dev, port_name, name_match);
+	if (!port_dev) {
+		gnss_cmdline_err("no port '%s'\n", port_name);
+		goto err_free_serdev_dup;
+	}
+
+	/* Find the serdev device instance (e.g. serial0-0) */
+	serdev_dev = device_find_child(port_dev, serdev_name, name_match);
+	if (!serdev_dev) {
+		gnss_cmdline_err("no serdev '%s'\n", serdev_name);
+		goto err_free_serdev_dup;
+	}
+
+	gserial = gnss_serial_allocate(to_serdev_device(serdev_dev), 0);
+	if (IS_ERR(gserial)) {
+		err = PTR_ERR(gserial);
+		goto err_free_serdev_dup;
+	}
+
+	gserial->gdev->type = type;
+
+	err = gnss_serial_register(gserial);
+	if (err) {
+		gnss_serial_free(gserial);
+		goto err_free_serdev_dup;
+	}
+
+	serdev_device = to_serdev_device(serdev_dev);
+	err = 0;
+err_free_serdev_dup:
+	kfree(serdev_dup);
+	return err;
+}
+
+static void __exit gnss_cmdline_exit(void)
+{
+	struct gnss_serial *gserial;
+
+	if (!serdev_device)
+		return;
+
+	gserial = serdev_device_get_drvdata(serdev_device);
+
+	gnss_serial_deregister(gserial);
+	gnss_serial_free(gserial);
+}
+
+module_init(gnss_cmdline_init);
+module_exit(gnss_cmdline_exit);
+
+MODULE_AUTHOR("Alistair Delva <adelva@google.com>");
+MODULE_DESCRIPTION("GNSS command line driver");
+MODULE_LICENSE("GPL v2");