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Subject[PATCH 5/6] gnss: motmdm: Add support for Motorola Mapphone MDM6600 modem
Date
Motorola is using a custom TS 27.010 based serial port line discipline
for various devices on the modem. These devices can be accessed on
dedicated channels using Linux kernel serdev-ngsm driver.

For the GNSS on these devices, we need to kick the GNSS device at a
desired rate. Otherwise the GNSS device stops sending data after a
few minutes. The rate we poll data defaults to 1000 ms, and can be
specified with a module option rate_ms between 1 to 16 seconds.

Note that AGPS with xtra2.bin is not yet supported, so getting a fix
can take quite a while. And a recent gpsd is needed to parse the
$GNGNS output, and to properly handle the /dev/gnss0 character device.
I've confirmed it works properly with gpsd-3.20.

Tested-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>
---
drivers/gnss/Kconfig | 8 +
drivers/gnss/Makefile | 3 +
drivers/gnss/motmdm.c | 419 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 430 insertions(+)
create mode 100644 drivers/gnss/motmdm.c

diff --git a/drivers/gnss/Kconfig b/drivers/gnss/Kconfig
--- a/drivers/gnss/Kconfig
+++ b/drivers/gnss/Kconfig
@@ -13,6 +13,14 @@ menuconfig GNSS

if GNSS

+config GNSS_MOTMDM
+ tristate "Motorola Modem TS 27.010 serdev GNSS receiver support"
+ depends on SERIAL_DEV_N_GSM
+ ---help---
+ Say Y here if you have a Motorola modem using TS 27.010 line
+ discipline for GNSS such as a Motorola Mapphone series device
+ like Droid 4.
+
config GNSS_SERIAL
tristate

diff --git a/drivers/gnss/Makefile b/drivers/gnss/Makefile
--- a/drivers/gnss/Makefile
+++ b/drivers/gnss/Makefile
@@ -6,6 +6,9 @@
obj-$(CONFIG_GNSS) += gnss.o
gnss-y := core.o

+obj-$(CONFIG_GNSS_MOTMDM) += gnss-motmdm.o
+gnss-motmdm-y := motmdm.o
+
obj-$(CONFIG_GNSS_SERIAL) += gnss-serial.o
gnss-serial-y := serial.o

diff --git a/drivers/gnss/motmdm.c b/drivers/gnss/motmdm.c
new file mode 100644
--- /dev/null
+++ b/drivers/gnss/motmdm.c
@@ -0,0 +1,419 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Motorola Modem TS 27.010 serdev GNSS driver
+ *
+ * Copyright (C) 2018 - 2020 Tony Lindgren <tony@atomide.com>
+ *
+ * Based on drivers/gnss/sirf.c driver example:
+ * Copyright (C) 2018 Johan Hovold <johan@kernel.org>
+ */
+
+#include <linux/errno.h>
+#include <linux/gnss.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/serdev-gsm.h>
+#include <linux/slab.h>
+
+#define MOTMDM_GNSS_TIMEOUT 1000
+#define MOTMDM_GNSS_RATE 1000
+
+/*
+ * Motorola MDM GNSS device communicates over a dedicated TS 27.010 channel
+ * using custom data packets. The packets look like AT commands embedded into
+ * a Motorola invented packet using format like "U1234AT+MPDSTART=0,1,100,0".
+ * But it's not an AT compatible serial interface, it's a packet interface
+ * using AT like commands.
+ */
+#define MOTMDM_GNSS_HEADER_LEN 5 /* U1234 */
+#define MOTMDM_GNSS_RESP_LEN (MOTMDM_GNSS_HEADER_LEN + 4) /* U1234+MPD */
+#define MOTMDM_GNSS_DATA_LEN (MOTMDM_GNSS_RESP_LEN + 1) /* U1234~+MPD */
+#define MOTMDM_GNSS_STATUS_LEN (MOTMDM_GNSS_DATA_LEN + 7) /* STATUS= */
+#define MOTMDM_GNSS_NMEA_LEN (MOTMDM_GNSS_DATA_LEN + 8) /* NMEA=NN, */
+
+enum motmdm_gnss_status {
+ MOTMDM_GNSS_UNKNOWN,
+ MOTMDM_GNSS_INITIALIZED,
+ MOTMDM_GNSS_DATA_OR_TIMEOUT,
+ MOTMDM_GNSS_STARTED,
+ MOTMDM_GNSS_STOPPED,
+};
+
+struct motmdm_gnss_data {
+ struct gnss_device *gdev;
+ struct device *modem;
+ struct gsm_serdev_dlci dlci;
+ struct delayed_work restart_work;
+ struct mutex mutex; /* For modem commands */
+ ktime_t last_update;
+ int status;
+ unsigned char *buf;
+ size_t len;
+ wait_queue_head_t read_queue;
+ unsigned int parsed:1;
+};
+
+static unsigned int rate_ms = MOTMDM_GNSS_RATE;
+module_param(rate_ms, uint, 0644);
+MODULE_PARM_DESC(rate_ms, "GNSS refresh rate between 1000 and 16000 ms (default 1000 ms)");
+
+/*
+ * Note that multiple commands can be sent in series with responses coming
+ * out-of-order. For GNSS, we don't need to care about the out-of-order
+ * responses, and can assume we have at most one command active at a time.
+ * For the commands, can use just a jiffies base packet ID and let the modem
+ * sort out the ID conflicts with the modem's unsolicited message ID
+ * numbering.
+ */
+static int motmdm_gnss_send_command(struct motmdm_gnss_data *ddata,
+ const u8 *buf, int len)
+{
+ struct gnss_device *gdev = ddata->gdev;
+ const int timeout_ms = 1000;
+ unsigned char cmd[128];
+ int ret, cmdlen;
+
+ cmdlen = len + 5 + 1;
+ if (cmdlen > 128)
+ return -EINVAL;
+
+ mutex_lock(&ddata->mutex);
+ memset(ddata->buf, 0, ddata->len);
+ ddata->parsed = false;
+ snprintf(cmd, cmdlen, "U%04li%s", jiffies % 10000, buf);
+ ret = serdev_ngsm_write(ddata->modem, &ddata->dlci, cmd, cmdlen);
+ if (ret < 0)
+ goto out_unlock;
+
+ ret = wait_event_timeout(ddata->read_queue, ddata->parsed,
+ msecs_to_jiffies(timeout_ms));
+ if (ret == 0) {
+ ret = -ETIMEDOUT;
+ goto out_unlock;
+ } else if (ret < 0) {
+ goto out_unlock;
+ }
+
+ if (!strstr(ddata->buf, ":OK")) {
+ dev_err(&gdev->dev, "command %s error %s\n",
+ cmd, ddata->buf);
+ ret = -EPIPE;
+ }
+
+ ret = len;
+
+out_unlock:
+ mutex_unlock(&ddata->mutex);
+
+ return ret;
+}
+
+/*
+ * Android uses AT+MPDSTART=0,1,100,0 which starts GNSS for a while,
+ * and then GNSS needs to be kicked with an AT command based on a
+ * status message.
+ */
+static void motmdm_gnss_restart(struct work_struct *work)
+{
+ struct motmdm_gnss_data *ddata =
+ container_of(work, struct motmdm_gnss_data,
+ restart_work.work);
+ struct gnss_device *gdev = ddata->gdev;
+ const unsigned char *cmd = "AT+MPDSTART=0,1,100,0";
+ int error;
+
+ ddata->last_update = ktime_get();
+
+ error = motmdm_gnss_send_command(ddata, cmd, strlen(cmd));
+ if (error < 0) {
+ /* Timeouts can happen, don't warn and try again */
+ if (error != -ETIMEDOUT)
+ dev_warn(&gdev->dev, "%s: could not start: %i\n",
+ __func__, error);
+
+ schedule_delayed_work(&ddata->restart_work,
+ msecs_to_jiffies(MOTMDM_GNSS_RATE));
+
+ return;
+ }
+}
+
+static void motmdm_gnss_start(struct gnss_device *gdev, int delay_ms)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ ktime_t now, next, delta;
+ int next_ms;
+
+ now = ktime_get();
+ next = ktime_add_ms(ddata->last_update, delay_ms);
+ delta = ktime_sub(next, now);
+ next_ms = ktime_to_ms(delta);
+
+ if (next_ms < 0)
+ next_ms = 0;
+ if (next_ms > delay_ms)
+ next_ms = delay_ms;
+
+ schedule_delayed_work(&ddata->restart_work, msecs_to_jiffies(next_ms));
+}
+
+static int motmdm_gnss_stop(struct gnss_device *gdev)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ const unsigned char *cmd = "AT+MPDSTOP";
+
+ cancel_delayed_work_sync(&ddata->restart_work);
+
+ return motmdm_gnss_send_command(ddata, cmd, strlen(cmd));
+}
+
+static int motmdm_gnss_init(struct gnss_device *gdev)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ const unsigned char *cmd = "AT+MPDINIT=1";
+ int error;
+
+ error = motmdm_gnss_send_command(ddata, cmd, strlen(cmd));
+ if (error < 0)
+ return error;
+
+ motmdm_gnss_start(gdev, 0);
+
+ return 0;
+}
+
+static int motmdm_gnss_finish(struct gnss_device *gdev)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ const unsigned char *cmd = "AT+MPDINIT=0";
+ int error;
+
+ error = motmdm_gnss_stop(gdev);
+ if (error < 0)
+ return error;
+
+ return motmdm_gnss_send_command(ddata, cmd, strlen(cmd));
+}
+
+static int motmdm_gnss_receive_data(struct gsm_serdev_dlci *dlci,
+ const unsigned char *buf,
+ size_t len)
+{
+ struct gnss_device *gdev = dlci->drvdata;
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ const unsigned char *msg;
+ size_t msglen;
+ int error = 0;
+
+ if (len <= MOTMDM_GNSS_RESP_LEN)
+ return 0;
+
+ /* Handle U1234+MPD style command response */
+ if (buf[MOTMDM_GNSS_HEADER_LEN] != '~') {
+ msg = buf + MOTMDM_GNSS_RESP_LEN;
+ strncpy(ddata->buf, msg, len - MOTMDM_GNSS_RESP_LEN);
+ ddata->parsed = true;
+ wake_up(&ddata->read_queue);
+
+ return len;
+ }
+
+ if (len <= MOTMDM_GNSS_DATA_LEN)
+ return 0;
+
+ /* Handle U1234~+MPD style unsolicted message */
+ switch (buf[MOTMDM_GNSS_DATA_LEN]) {
+ case 'N': /* UNNNN~+MPDNMEA=NN, */
+ msg = buf + MOTMDM_GNSS_NMEA_LEN;
+ msglen = len - MOTMDM_GNSS_NMEA_LEN;
+
+ /*
+ * Firmware bug: Strip out extra duplicate line break always
+ * in the data
+ */
+ msglen--;
+
+ /*
+ * Firmware bug: Strip out extra data based on an
+ * earlier line break in the data
+ */
+ if (msg[msglen - 5 - 1] == 0x0a)
+ msglen -= 5;
+
+ error = gnss_insert_raw(gdev, msg, msglen);
+ break;
+ case 'S': /* UNNNN~+MPDSTATUS=N,NN */
+ msg = buf + MOTMDM_GNSS_STATUS_LEN;
+ msglen = len - MOTMDM_GNSS_STATUS_LEN;
+
+ switch (msg[0]) {
+ case '1':
+ ddata->status = MOTMDM_GNSS_INITIALIZED;
+ break;
+ case '2':
+ ddata->status = MOTMDM_GNSS_DATA_OR_TIMEOUT;
+ if (rate_ms < MOTMDM_GNSS_RATE)
+ rate_ms = MOTMDM_GNSS_RATE;
+ if (rate_ms > 16 * MOTMDM_GNSS_RATE)
+ rate_ms = 16 * MOTMDM_GNSS_RATE;
+ motmdm_gnss_start(gdev, rate_ms);
+ break;
+ case '3':
+ ddata->status = MOTMDM_GNSS_STARTED;
+ break;
+ case '4':
+ ddata->status = MOTMDM_GNSS_STOPPED;
+ break;
+ default:
+ ddata->status = MOTMDM_GNSS_UNKNOWN;
+ break;
+ }
+ break;
+ case 'X': /* UNNNN~+MPDXREQ=N for updated xtra2.bin needed */
+ default:
+ break;
+ }
+
+ return len;
+}
+
+static int motmdm_gnss_open(struct gnss_device *gdev)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ struct gsm_serdev_dlci *dlci = &ddata->dlci;
+ int error;
+
+ dlci->drvdata = gdev;
+ dlci->receive_buf = motmdm_gnss_receive_data;
+
+ error = serdev_ngsm_register_dlci(ddata->modem, dlci);
+ if (error)
+ return error;
+
+ error = motmdm_gnss_init(gdev);
+ if (error) {
+ serdev_ngsm_unregister_dlci(ddata->modem, dlci);
+
+ return error;
+ }
+
+ return 0;
+}
+
+static void motmdm_gnss_close(struct gnss_device *gdev)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+ struct gsm_serdev_dlci *dlci = &ddata->dlci;
+ int error;
+
+ dlci->receive_buf = NULL;
+ error = motmdm_gnss_finish(gdev);
+ if (error < 0)
+ dev_warn(&gdev->dev, "%s: close failed: %i\n",
+ __func__, error);
+
+ serdev_ngsm_unregister_dlci(ddata->modem, dlci);
+}
+
+static int motmdm_gnss_write_raw(struct gnss_device *gdev,
+ const unsigned char *buf,
+ size_t count)
+{
+ struct motmdm_gnss_data *ddata = gnss_get_drvdata(gdev);
+
+ return serdev_ngsm_write(ddata->modem, &ddata->dlci, buf, count);
+}
+
+static const struct gnss_operations motmdm_gnss_ops = {
+ .open = motmdm_gnss_open,
+ .close = motmdm_gnss_close,
+ .write_raw = motmdm_gnss_write_raw,
+};
+
+static int motmdm_gnss_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct motmdm_gnss_data *ddata;
+ struct gnss_device *gdev;
+ u32 line;
+ int ret;
+
+ ddata = devm_kzalloc(dev, sizeof(*ddata), GFP_KERNEL);
+ if (!ddata)
+ return -ENOMEM;
+
+ ret = of_property_read_u32(dev->of_node, "reg", &line);
+ if (ret)
+ return ret;
+
+ if (!line)
+ return -EINVAL;
+
+ ddata->dlci.line = line;
+ ddata->modem = dev->parent;
+ ddata->len = PAGE_SIZE;
+ mutex_init(&ddata->mutex);
+ INIT_DELAYED_WORK(&ddata->restart_work, motmdm_gnss_restart);
+ init_waitqueue_head(&ddata->read_queue);
+
+ ddata->buf = devm_kzalloc(dev, ddata->len, GFP_KERNEL);
+ if (!ddata->buf)
+ return -ENOMEM;
+
+ platform_set_drvdata(pdev, ddata);
+
+ gdev = gnss_allocate_device(dev);
+ if (!gdev)
+ return -ENOMEM;
+
+ gdev->type = GNSS_TYPE_NMEA;
+ gdev->ops = &motmdm_gnss_ops;
+ gnss_set_drvdata(gdev, ddata);
+ ddata->gdev = gdev;
+
+ ret = gnss_register_device(gdev);
+ if (ret)
+ goto err_put_device;
+
+ return 0;
+
+err_put_device:
+ gnss_put_device(ddata->gdev);
+
+ return ret;
+}
+
+static int motmdm_gnss_remove(struct platform_device *pdev)
+{
+ struct motmdm_gnss_data *data = platform_get_drvdata(pdev);
+
+ gnss_deregister_device(data->gdev);
+ gnss_put_device(data->gdev);
+
+ return 0;
+};
+
+#ifdef CONFIG_OF
+static const struct of_device_id motmdm_gnss_of_match[] = {
+ { .compatible = "motorola,mapphone-mdm6600-gnss" },
+ {},
+};
+MODULE_DEVICE_TABLE(of, motmdm_gnss_of_match);
+#endif
+
+static struct platform_driver motmdm_gnss_driver = {
+ .driver = {
+ .name = "gnss-mot-mdm6600",
+ .of_match_table = of_match_ptr(motmdm_gnss_of_match),
+ },
+ .probe = motmdm_gnss_probe,
+ .remove = motmdm_gnss_remove,
+};
+module_platform_driver(motmdm_gnss_driver);
+
+MODULE_AUTHOR("Tony Lindgren <tony@atomide.com>");
+MODULE_DESCRIPTION("Motorola Mapphone MDM6600 GNSS receiver driver");
+MODULE_LICENSE("GPL v2");
--
2.26.2
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