Hi Greg,

On Tue, Jan 13, 2015 at 5:33 PM, Greg Kroah-Hartman
[off-list ref] wrote:

On Tue, Jan 13, 2015 at 05:16:42PM -0800, Felipe F. Tonello wrote:

quoted

This driver will basically translate serial communication to i2c communication
between the user-space and the GPS module.

It creates a /dev/ttyS device node.

There are specific tty termios flags in order to the tty line discipliner not
to change the date it is pushed to user space.

I don't understand this sentance, what date?  What is pushed where?
What termios files?  What is a "discipliner"?

Some typos here, I will fix it and try to explain it better.

quoted

That is necessary so the NMEA
data is not corrupted.
* iflags: added IGNCR: Ignore carriage return on input.
* oflags: removed ONLCR: (XSI) Map NL to CR-NL on output.

Signed-off-by: Felipe F. Tonello <redacted>
---
 drivers/tty/serial/Kconfig          |   9 ++
 drivers/tty/serial/Makefile         |   1 +
 drivers/tty/serial/ublox6-gps-i2c.c | 245 ++++++++++++++++++++++++++++++++++++
 3 files changed, 255 insertions(+)
 create mode 100644 drivers/tty/serial/ublox6-gps-i2c.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 26cec64..49913eb 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig

@@ -1552,6 +1552,15 @@ config SERIAL_MEN_Z135
        This driver can also be build as a module. If so, the module will be called
        men_z135_uart.ko

+config SERIAL_UBLOX_GPS
+     tristate "u-blox 6 I2C GPS support"
+     depends on I2C
+     default n
+     help
+       This driver uses i2c to communicate with the u-blox 6 GPS module
+       and has a serial tty device interface to the user-space, making
+       it easy to read/write data from/to the GPS.
+
 endmenu

 config SERIAL_MCTRL_GPIO

diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index 0080cc3..cba2b5c 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile

@@ -92,6 +92,7 @@ obj-$(CONFIG_SERIAL_ARC)    += arc_uart.o
 obj-$(CONFIG_SERIAL_RP2)     += rp2.o
 obj-$(CONFIG_SERIAL_FSL_LPUART)      += fsl_lpuart.o
 obj-$(CONFIG_SERIAL_MEN_Z135)        += men_z135_uart.o
+obj-$(CONFIG_SERIAL_UBLOX_GPS) += ublox6-gps-i2c.o

 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)      += serial_mctrl_gpio.o

diff --git a/drivers/tty/serial/ublox6-gps-i2c.c b/drivers/tty/serial/ublox6-gps-i2c.c
new file mode 100644
index 0000000..16dd1cf
--- /dev/null
+++ b/drivers/tty/serial/ublox6-gps-i2c.c

@@ -0,0 +1,245 @@
+/* u-blox 6 I2C GPS driver
+ *
+ * Copyright (C) 2015 Felipe F. Tonello <eu@felipetonello.com>
+ *
+ * Driver that translates a serial tty GPS device to a i2c GPS device

I don't think there is a "serial tty GPS device" here, right?

No, it is a i2c device driver that translates to tty serial.

quoted

+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/i2c.h>
+#include <linux/workqueue.h>
+
+/*
+ * Version Information
+ */
+#define DRIVER_VERSION "v0.1"
+#define DRIVER_DESC "u-blox 6 I2C GPS driver"
+
+#define UBLOX_GPS_MAJOR 0
+#define UBLOX_GPS_NUM 1 /* Only support 1 GPS at a time */
+
+/* By default u-blox GPS fill its buffer every 1 second (1000 msecs) */
+#define READ_TIME 1000
+
+static struct tty_port *ublox_gps_tty_port;
+static struct i2c_client *ublox_gps_i2c_client;

Why only one device/client?  Why can't you have more than one in the
system?  Please don't make this work for only one device, these can all
be device-private.

True.

quoted

+static int ublox_gps_is_open;

Why do you need this?  And again, don't make it global for the whole
driver, but unique per-device

quoted

+static struct file *ublox_gps_filp;

I don't understand why you even need this, what problem is this solving?

See tty close operation.

quoted

+static void ublox_gps_read_worker(struct work_struct *private);
+
+static DECLARE_DELAYED_WORK(ublox_gps_wq, ublox_gps_read_worker);

Again, make device-specific.

quoted

+static void ublox_gps_read_worker(struct work_struct *private)
+{
+     s32 gps_buf_size, buf_size = 0;
+     u8 *buf;
+
+     if (!ublox_gps_is_open)
+             return;

How can this happen?

If the tty device is closed and there is a scheduled workqueue, then
this might happen.

quoted

+
+     /* check if driver was removed */
+     if (!ublox_gps_i2c_client)
+             return;

How can this happen?

If tty device is open and user removes the module (if it is a module)
and there is a scheduled workqueue, then this might happen.

quoted

+
+     gps_buf_size = i2c_smbus_read_word_data(ublox_gps_i2c_client, 0xfd);
+     if (gps_buf_size < 0) {
+             dev_warn(&ublox_gps_i2c_client->dev, KBUILD_MODNAME ": couldn't read register(0xfd) from GPS.\n");

Something to be fixed for all of your dev_*() calls, don't put
KBUILD_MODNAME, it's not needed as dev_* handles everything properly to
point to the specific driver and device that created the message.

Got it.

quoted

+             /* try one more time */
+             goto end;
+     }
+
+     /* 0xfd is the MSB and 0xfe is the LSB */
+     gps_buf_size = ((gps_buf_size & 0xf) << 8) | ((gps_buf_size & 0xf0) >> 8);

I don't understand the comment here.

I'll improve.

quoted

+
+     if (gps_buf_size > 0) {
+
+             buf = kcalloc(gps_buf_size, sizeof(*buf), GFP_KERNEL);
+             if (!buf) {
+                     dev_warn(&ublox_gps_i2c_client->dev, KBUILD_MODNAME ": couldn't allocate memory.\n");

No need to send any error if memory is gone, that already happened in
the syslog.

Ok.

quoted

+                     /* try one more time */
+                     goto end;
+             }
+
+             do {
+                     buf_size = i2c_master_recv(ublox_gps_i2c_client, (char *)buf, gps_buf_size);
+                     if (buf_size < 0) {
+                             dev_warn(&ublox_gps_i2c_client->dev, KBUILD_MODNAME ": couldn't read data from GPS.\n");
+                             kfree(buf);
+                             /* try one more time */
+                             goto end;
+                     }
+
+                     tty_insert_flip_string(ublox_gps_tty_port, buf, buf_size);
+
+                     gps_buf_size -= buf_size;
+
+                     /* There is a small chance that we need to split the data over
+                        several buffers. If this is the case we must loop */
+             } while (unlikely(gps_buf_size > 0));
+
+             tty_flip_buffer_push(ublox_gps_tty_port);
+
+             kfree(buf);
+     }
+
+end:
+     /* resubmit the workqueue again */
+     schedule_delayed_work(&ublox_gps_wq, msecs_to_jiffies(READ_TIME)); /* 1 sec delay */
+}
+
+static int ublox_gps_serial_open(struct tty_struct *tty, struct file *filp)
+{
+     if (ublox_gps_is_open)
+             return -EBUSY;
+
+     ublox_gps_filp = filp;
+     ublox_gps_tty_port = tty->port;
+     ublox_gps_tty_port->low_latency = true; /* make sure we push data immediately */
+     ublox_gps_is_open = true;
+
+     schedule_delayed_work(&ublox_gps_wq, 0);
+
+     return 0;
+}
+
+static void ublox_gps_serial_close(struct tty_struct *tty, struct file *filp)
+{
+     if (!ublox_gps_is_open)

How can this happen?

I am not sure. But it is better to check then having a unknown bug anyway.

quoted

+             return;
+
+     /* avoid stop when the denied (in open) file structure closes itself */
+     if (ublox_gps_filp != filp)
+             return;

I don't understand, how can something "close itself"?

What happens is that this callback is called if a user tries to open
two ttyS for the GPS. The second will fail, calling the close, thus
calling this callback with different filp.
So I need to check if the close was really called by the first ttyS user.

quoted

+
+     ublox_gps_is_open = false;
+     ublox_gps_filp = NULL;
+     ublox_gps_tty_port = NULL;
+}
+
+static int ublox_gps_serial_write(struct tty_struct *tty, const unsigned char *buf,
+     int count)
+{
+     if (!ublox_gps_is_open)
+             return 0;
+
+     /* check if driver was removed */
+     if (!ublox_gps_i2c_client)
+             return 0;
+
+     /* we don't write back to the GPS so just return same value here */
+     return count;
+}

So write does nothing, why even have it at all?

Because for some reason the tty layer was calling it anyway.

quoted

+static int ublox_gps_write_room(struct tty_struct *tty)
+{
+     if (!ublox_gps_is_open)
+             return 0;
+
+     /* check if driver was removed */
+     if (!ublox_gps_i2c_client)
+             return 0;
+
+     /* we don't write back to the GPS so just return some value here */
+     return 1024;

Why have this function at all if it does nothing?

Same as the write.

quoted

+}
+
+static const struct tty_operations ublox_gps_serial_ops = {
+     .open = ublox_gps_serial_open,
+     .close = ublox_gps_serial_close,
+     .write = ublox_gps_serial_write,
+     .write_room = ublox_gps_write_room,
+};
+
+static struct tty_driver *ublox_gps_tty_driver;
+
+static int ublox_gps_probe(struct i2c_client *client,
+     const struct i2c_device_id *id)
+{
+     int result = 0;
+
+     ublox_gps_tty_driver = alloc_tty_driver(UBLOX_GPS_NUM);
+     if (!ublox_gps_tty_driver)
+             return -ENOMEM;
+
+     ublox_gps_tty_driver->owner = THIS_MODULE;
+     ublox_gps_tty_driver->driver_name = "ublox_gps";
+     ublox_gps_tty_driver->name = "ttyS";
+     ublox_gps_tty_driver->major = UBLOX_GPS_MAJOR;
+     ublox_gps_tty_driver->minor_start = 0;
+     ublox_gps_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
+     ublox_gps_tty_driver->subtype = SERIAL_TYPE_NORMAL;
+     ublox_gps_tty_driver->flags = TTY_DRIVER_REAL_RAW;
+     ublox_gps_tty_driver->init_termios = tty_std_termios;
+     ublox_gps_tty_driver->init_termios.c_iflag = IGNCR | IXON;
+     ublox_gps_tty_driver->init_termios.c_oflag = OPOST;
+     ublox_gps_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD |
+             HUPCL | CLOCAL;
+     ublox_gps_tty_driver->init_termios.c_ispeed = 9600;
+     ublox_gps_tty_driver->init_termios.c_ospeed = 9600;
+     tty_set_operations(ublox_gps_tty_driver, &ublox_gps_serial_ops);
+     result = tty_register_driver(ublox_gps_tty_driver);
+     if (result) {
+             dev_err(&ublox_gps_i2c_client->dev, KBUILD_MODNAME ": %s - tty_register_driver failed\n",
+                     __func__);
+             goto err;
+     }
+
+     ublox_gps_i2c_client = client;
+     ublox_gps_filp = NULL;
+     ublox_gps_tty_port = NULL;
+     ublox_gps_is_open = false;
+
+     /* i2c_set_clientdata(client, NULL); */
+
+     dev_info(&ublox_gps_i2c_client->dev, KBUILD_MODNAME ": " DRIVER_VERSION ": "
+             DRIVER_DESC "\n");

Be quiet for "normal" operations please, your driver should never send
anything to the kernel log unless some error happens.

Got it.

thanks,

greg k-h