[PATCH 2/3] TTY: add support for tty_slave devices.

NeilBrown
2015-03-18T06:00:31Z

A "tty slave" is a device connected via UART.
Such a device may need its own driver, e.g. for powering
it up on tty open and powering it down on tty release.

tty-slave is a new bus-type which drivers can be written and devices
created.

A "tty slave" device is declared as a child of the uart in
device-tree:

&uart1 {
bluetooth {
compatible = "wi2wi,w2cbw003";
vdd-supply = <&vaux4>;
};
};

This device will be inserted in the driver-model tree between the uart
and the tty.

The tty-slave driver can replace any of the tty_operations functions
so a call by the tty can be intercepted before being handled by the uart.

Signed-off-by: NeilBrown <neil@brown.name>
---
drivers/tty/Kconfig | 1
drivers/tty/Makefile | 1
drivers/tty/slave/Kconfig | 7 ++
drivers/tty/slave/Makefile | 2 +
drivers/tty/slave/tty_slave_core.c | 136 ++++++++++++++++++++++++++++++++++++
drivers/tty/tty_io.c | 54 +++++++++++---
include/linux/tty.h | 1
include/linux/tty_slave.h | 26 +++++++
8 files changed, 215 insertions(+), 13 deletions(-)
create mode 100644 drivers/tty/slave/Kconfig
create mode 100644 drivers/tty/slave/Makefile
create mode 100644 drivers/tty/slave/tty_slave_core.c
create mode 100644 include/linux/tty_slave.h

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index b24aa010f68c..f9155a45ee7c 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -419,4 +419,5 @@ config DA_CONSOLE
help
This enables a console on a Dash channel.

+source drivers/tty/slave/Kconfig
endif # TTY
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 58ad1c05b7f8..ec57846eac29 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -31,3 +31,4 @@ obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o
obj-$(CONFIG_DA_TTY) += metag_da.o

obj-y += ipwireless/
+obj-y += slave/
diff --git a/drivers/tty/slave/Kconfig b/drivers/tty/slave/Kconfig
new file mode 100644
index 000000000000..3976760c2e28
--- /dev/null
+++ b/drivers/tty/slave/Kconfig
@@ -0,0 +1,7 @@
+menuconfig TTY_SLAVE
+ tristate "TTY slave devices"
+ depends on OF
+ help
+ Devices which attach via a uart, but need extra
+ driver support for power management etc.
+
diff --git a/drivers/tty/slave/Makefile b/drivers/tty/slave/Makefile
new file mode 100644
index 000000000000..65669acb392e
--- /dev/null
+++ b/drivers/tty/slave/Makefile
@@ -0,0 +1,2 @@
+
+obj-$(CONFIG_TTY_SLAVE) += tty_slave_core.o
diff --git a/drivers/tty/slave/tty_slave_core.c b/drivers/tty/slave/tty_slave_core.c
new file mode 100644
index 000000000000..6218ea5bb69e
--- /dev/null
+++ b/drivers/tty/slave/tty_slave_core.c
@@ -0,0 +1,136 @@
+/*
+ * tty-slave-core - device bus for tty slaves
+ *
+ * Copyright (C) 2015 NeilBrown <neil@brown.name>
+ *
+ * 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.
+ */
+
+/*
+ * A "tty-slave" is a device permanently attached to a particularly
+ * tty, typically wired to a UART.
+ * A tty-slave has two particular roles.
+ * Firstly it can intercept any tty_operations to provide extra control
+ * of the device. For example it might intercept "open" and "close"
+ * in order to power the device up and down. It might intercept
+ * "hangup" to toggle a reset line on the device.
+ *
+ * Secondly it appears as a parent of the tty in the device model, so
+ * that any attributes it presents are visible to udev when the tty
+ * is added. This allows udev to start appropriate handlers such as
+ * hciattach or inputattach.
+ *
+ * tty-slave devices must be described in devicetree as a child node
+ * of the node which described the parent of the tty, typically a
+ * UART.
+ * If such a child is present, the tty device will not be registered
+ * until the slave device is fully probed and initialized.
+ */
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/device.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_slave.h>
+
+
+static int tty_slave_match(struct device *dev, struct device_driver *drv)
+{
+ return of_driver_match_device(dev, drv);
+}
+
+static void tty_slave_release(struct device *dev)
+{
+ kfree(dev);
+}
+
+struct bus_type tty_slave_bus_type = {
+ .name = "tty-slave",
+ .match = tty_slave_match,
+};
+
+int tty_slave_register(struct device *parent, struct device_node *node,
+ struct device *tty, struct tty_driver *drv)
+{
+ struct tty_slave *slave;
+ int retval;
+
+ if (!of_get_property(node, "compatible", NULL))
+ return -ENODEV;
+
+ slave = kzalloc(sizeof(*slave), GFP_KERNEL);
+ if (!slave)
+ return -ENOMEM;
+
+ slave->dev.bus = &tty_slave_bus_type;
+ slave->dev.parent = parent;
+ slave->dev.release = tty_slave_release;
+ slave->dev.of_node = of_node_get(node);
+ dev_set_name(&slave->dev, "%s", node->name);
+ slave->tty_dev = tty;
+ slave->tty_drv = drv;
+ slave->ops = *drv->ops;
+ retval = device_register(&slave->dev);
+ if (retval) {
+ of_node_put(node);
+ kfree(slave);
+ }
+ return retval;
+}
+EXPORT_SYMBOL(tty_slave_register);
+
+void tty_slave_activate(struct tty_struct *tty)
+{
+ struct device *parent = NULL;
+ if (tty->dev)
+ parent = tty->dev->parent;
+ if (parent &&
+ parent->bus == &tty_slave_bus_type)
+ {
+ struct tty_slave *dev =
+ container_of(parent, struct tty_slave, dev);
+ tty->ops = &dev->ops;
+ }
+}
+EXPORT_SYMBOL(tty_slave_activate);
+
+int tty_slave_finalize(struct tty_slave *slave)
+{
+ slave->tty_dev->parent = &slave->dev;
+ return tty_register_finalize(slave->tty_drv,
+ slave->tty_dev);
+}
+EXPORT_SYMBOL(tty_slave_finalize);
+
+int tty_slave_driver_register(struct device_driver *drv)
+{
+ drv->bus = &tty_slave_bus_type;
+ return driver_register(drv);
+}
+EXPORT_SYMBOL(tty_slave_driver_register);
+
+static int __init tty_slave_init(void)
+{
+ return bus_register(&tty_slave_bus_type);
+}
+
+static void __exit tty_slave_exit(void)
+{
+ bus_unregister(&tty_slave_bus_type);
+}
+
+postcore_initcall(tty_slave_init);
+module_exit(tty_slave_exit);
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 27632ad17d6f..2b2d3b549a58 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -95,6 +95,8 @@
#include <linux/seq_file.h>
#include <linux/serial.h>
#include <linux/ratelimit.h>
+#include <linux/of.h>
+#include <linux/tty_slave.h>

#include <linux/uaccess.h>

@@ -3124,6 +3126,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
tty->index = idx;
tty_line_name(driver, idx, tty->name);
tty->dev = tty_get_device(tty);
+ tty_slave_activate(tty);

return tty;
}
@@ -3205,6 +3208,29 @@ static void tty_device_create_release(struct device *dev)
kfree(dev);
}

+int tty_register_finalize(struct tty_driver *driver, struct device *dev)
+{
+ int retval;
+ bool cdev = false;
+ int index = dev->devt - MKDEV(driver->major,
+ driver->minor_start);
+ printk("REGISTER %d %d 0x%x %d\n", driver->major, driver->minor_start, dev->devt, index);
+ if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
+ retval = tty_cdev_add(driver,
+ dev->devt,
+ index, 1);
+ if (retval)
+ return retval;
+ cdev = true;
+ }
+ retval = device_register(dev);
+ if (retval == 0)
+ return 0;
+ if (cdev)
+ cdev_del(&driver->cdevs[index]);
+ return retval;
+}
+EXPORT_SYMBOL(tty_register_finalize);
/**
* tty_register_device_attr - register a tty device
* @driver: the tty driver that describes the tty device
@@ -3234,7 +3260,8 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
dev_t devt = MKDEV(driver->major, driver->minor_start) + index;
struct device *dev = NULL;
int retval = -ENODEV;
- bool cdev = false;
+ struct device_node *node;
+ bool slave_registered = false;

if (index >= driver->num) {
printk(KERN_ERR "Attempt to register invalid tty line number "
@@ -3247,13 +3274,6 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
else
tty_line_name(driver, index, name);

- if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
- retval = tty_cdev_add(driver, devt, index, 1);
- if (retval)
- goto error;
- cdev = true;
- }
-
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev) {
retval = -ENOMEM;
@@ -3268,16 +3288,24 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
dev->groups = attr_grp;
dev_set_drvdata(dev, drvdata);

- retval = device_register(dev);
- if (retval)
- goto error;
+ if (device && device->of_node)
+ for_each_available_child_of_node(device->of_node, node) {
+ if (tty_slave_register(device, node, dev, driver) == 0)
+ slave_registered = true;
+ if (slave_registered)
+ break;
+ }
+
+ if (!slave_registered) {
+ retval = tty_register_finalize(driver, dev);
+ if (retval)
+ goto error;
+ }

return dev;

error:
put_device(dev);
- if (cdev)
- cdev_del(&driver->cdevs[index]);
return ERR_PTR(retval);
}
EXPORT_SYMBOL_GPL(tty_register_device_attr);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 04d5f1213700..efb4e053b856 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -373,6 +373,7 @@ extern void proc_clear_tty(struct task_struct *p);
extern struct tty_struct *get_current_tty(void);
/* tty_io.c */
extern int __init tty_init(void);
+extern int tty_register_finalize(struct tty_driver *driver, struct device *dev);
#else
static inline void console_init(void)
{ }
diff --git a/include/linux/tty_slave.h b/include/linux/tty_slave.h
new file mode 100644
index 000000000000..21bfd7c01a2e
--- /dev/null
+++ b/include/linux/tty_slave.h
@@ -0,0 +1,26 @@
+
+struct tty_slave {
+ struct device *tty_dev;
+ struct tty_driver *tty_drv;
+ struct tty_operations ops;
+ struct device dev;
+};
+
+int tty_slave_finalize(struct tty_slave *slave);
+int tty_slave_driver_register(struct device_driver *drv);
+#if config_enabled(CONFIG_TTY_SLAVE)
+void tty_slave_activate(struct tty_struct *tty);
+int tty_slave_register(struct device *parent, struct device_node *node,
+ struct device *tty, struct tty_driver *drv);
+#else
+static inline void tty_slave_activate(struct tty_struct *tty)
+{
+}
+static inline int tty_slave_register(struct device *parent,
+ struct device_node *node,
+ struct device *tty,
+ struct tty_driver *drv)
+{
+ return -ENODEV;
+}
+#endif