1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
330 lines
9.9 KiB
Text
330 lines
9.9 KiB
Text
|
|
Low Level Serial API
|
|
--------------------
|
|
|
|
|
|
$Id: driver,v 1.10 2002/07/22 15:27:30 rmk Exp $
|
|
|
|
|
|
This document is meant as a brief overview of some aspects of the new serial
|
|
driver. It is not complete, any questions you have should be directed to
|
|
<rmk@arm.linux.org.uk>
|
|
|
|
The reference implementation is contained within serial_amba.c.
|
|
|
|
|
|
|
|
Low Level Serial Hardware Driver
|
|
--------------------------------
|
|
|
|
The low level serial hardware driver is responsible for supplying port
|
|
information (defined by uart_port) and a set of control methods (defined
|
|
by uart_ops) to the core serial driver. The low level driver is also
|
|
responsible for handling interrupts for the port, and providing any
|
|
console support.
|
|
|
|
|
|
Console Support
|
|
---------------
|
|
|
|
The serial core provides a few helper functions. This includes identifing
|
|
the correct port structure (via uart_get_console) and decoding command line
|
|
arguments (uart_parse_options).
|
|
|
|
|
|
Locking
|
|
-------
|
|
|
|
It is the responsibility of the low level hardware driver to perform the
|
|
necessary locking using port->lock. There are some exceptions (which
|
|
are described in the uart_ops listing below.)
|
|
|
|
There are three locks. A per-port spinlock, a per-port tmpbuf semaphore,
|
|
and an overall semaphore.
|
|
|
|
From the core driver perspective, the port->lock locks the following
|
|
data:
|
|
|
|
port->mctrl
|
|
port->icount
|
|
info->xmit.head (circ->head)
|
|
info->xmit.tail (circ->tail)
|
|
|
|
The low level driver is free to use this lock to provide any additional
|
|
locking.
|
|
|
|
The core driver uses the info->tmpbuf_sem lock to prevent multi-threaded
|
|
access to the info->tmpbuf bouncebuffer used for port writes.
|
|
|
|
The port_sem semaphore is used to protect against ports being added/
|
|
removed or reconfigured at inappropriate times.
|
|
|
|
|
|
uart_ops
|
|
--------
|
|
|
|
The uart_ops structure is the main interface between serial_core and the
|
|
hardware specific driver. It contains all the methods to control the
|
|
hardware.
|
|
|
|
tx_empty(port)
|
|
This function tests whether the transmitter fifo and shifter
|
|
for the port described by 'port' is empty. If it is empty,
|
|
this function should return TIOCSER_TEMT, otherwise return 0.
|
|
If the port does not support this operation, then it should
|
|
return TIOCSER_TEMT.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
This call must not sleep
|
|
|
|
set_mctrl(port, mctrl)
|
|
This function sets the modem control lines for port described
|
|
by 'port' to the state described by mctrl. The relevant bits
|
|
of mctrl are:
|
|
- TIOCM_RTS RTS signal.
|
|
- TIOCM_DTR DTR signal.
|
|
- TIOCM_OUT1 OUT1 signal.
|
|
- TIOCM_OUT2 OUT2 signal.
|
|
If the appropriate bit is set, the signal should be driven
|
|
active. If the bit is clear, the signal should be driven
|
|
inactive.
|
|
|
|
Locking: port->lock taken.
|
|
Interrupts: locally disabled.
|
|
This call must not sleep
|
|
|
|
get_mctrl(port)
|
|
Returns the current state of modem control inputs. The state
|
|
of the outputs should not be returned, since the core keeps
|
|
track of their state. The state information should include:
|
|
- TIOCM_DCD state of DCD signal
|
|
- TIOCM_CTS state of CTS signal
|
|
- TIOCM_DSR state of DSR signal
|
|
- TIOCM_RI state of RI signal
|
|
The bit is set if the signal is currently driven active. If
|
|
the port does not support CTS, DCD or DSR, the driver should
|
|
indicate that the signal is permanently active. If RI is
|
|
not available, the signal should not be indicated as active.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
This call must not sleep
|
|
|
|
stop_tx(port,tty_stop)
|
|
Stop transmitting characters. This might be due to the CTS
|
|
line becoming inactive or the tty layer indicating we want
|
|
to stop transmission.
|
|
|
|
tty_stop: 1 if this call is due to the TTY layer issuing a
|
|
TTY stop to the driver (equiv to rs_stop).
|
|
|
|
Locking: port->lock taken.
|
|
Interrupts: locally disabled.
|
|
This call must not sleep
|
|
|
|
start_tx(port,tty_start)
|
|
start transmitting characters. (incidentally, nonempty will
|
|
always be nonzero, and shouldn't be used - it will be dropped).
|
|
|
|
tty_start: 1 if this call was due to the TTY layer issuing
|
|
a TTY start to the driver (equiv to rs_start)
|
|
|
|
Locking: port->lock taken.
|
|
Interrupts: locally disabled.
|
|
This call must not sleep
|
|
|
|
stop_rx(port)
|
|
Stop receiving characters; the port is in the process of
|
|
being closed.
|
|
|
|
Locking: port->lock taken.
|
|
Interrupts: locally disabled.
|
|
This call must not sleep
|
|
|
|
enable_ms(port)
|
|
Enable the modem status interrupts.
|
|
|
|
Locking: port->lock taken.
|
|
Interrupts: locally disabled.
|
|
This call must not sleep
|
|
|
|
break_ctl(port,ctl)
|
|
Control the transmission of a break signal. If ctl is
|
|
nonzero, the break signal should be transmitted. The signal
|
|
should be terminated when another call is made with a zero
|
|
ctl.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
This call must not sleep
|
|
|
|
startup(port)
|
|
Grab any interrupt resources and initialise any low level driver
|
|
state. Enable the port for reception. It should not activate
|
|
RTS nor DTR; this will be done via a separate call to set_mctrl.
|
|
|
|
Locking: port_sem taken.
|
|
Interrupts: globally disabled.
|
|
|
|
shutdown(port)
|
|
Disable the port, disable any break condition that may be in
|
|
effect, and free any interrupt resources. It should not disable
|
|
RTS nor DTR; this will have already been done via a separate
|
|
call to set_mctrl.
|
|
|
|
Locking: port_sem taken.
|
|
Interrupts: caller dependent.
|
|
|
|
set_termios(port,termios,oldtermios)
|
|
Change the port parameters, including word length, parity, stop
|
|
bits. Update read_status_mask and ignore_status_mask to indicate
|
|
the types of events we are interested in receiving. Relevant
|
|
termios->c_cflag bits are:
|
|
CSIZE - word size
|
|
CSTOPB - 2 stop bits
|
|
PARENB - parity enable
|
|
PARODD - odd parity (when PARENB is in force)
|
|
CREAD - enable reception of characters (if not set,
|
|
still receive characters from the port, but
|
|
throw them away.
|
|
CRTSCTS - if set, enable CTS status change reporting
|
|
CLOCAL - if not set, enable modem status change
|
|
reporting.
|
|
Relevant termios->c_iflag bits are:
|
|
INPCK - enable frame and parity error events to be
|
|
passed to the TTY layer.
|
|
BRKINT
|
|
PARMRK - both of these enable break events to be
|
|
passed to the TTY layer.
|
|
|
|
IGNPAR - ignore parity and framing errors
|
|
IGNBRK - ignore break errors, If IGNPAR is also
|
|
set, ignore overrun errors as well.
|
|
The interaction of the iflag bits is as follows (parity error
|
|
given as an example):
|
|
Parity error INPCK IGNPAR
|
|
None n/a n/a character received
|
|
Yes n/a 0 character discarded
|
|
Yes 0 1 character received, marked as
|
|
TTY_NORMAL
|
|
Yes 1 1 character received, marked as
|
|
TTY_PARITY
|
|
|
|
Other flags may be used (eg, xon/xoff characters) if your
|
|
hardware supports hardware "soft" flow control.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
This call must not sleep
|
|
|
|
pm(port,state,oldstate)
|
|
Perform any power management related activities on the specified
|
|
port. State indicates the new state (defined by ACPI D0-D3),
|
|
oldstate indicates the previous state. Essentially, D0 means
|
|
fully on, D3 means powered down.
|
|
|
|
This function should not be used to grab any resources.
|
|
|
|
This will be called when the port is initially opened and finally
|
|
closed, except when the port is also the system console. This
|
|
will occur even if CONFIG_PM is not set.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
type(port)
|
|
Return a pointer to a string constant describing the specified
|
|
port, or return NULL, in which case the string 'unknown' is
|
|
substituted.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
release_port(port)
|
|
Release any memory and IO region resources currently in use by
|
|
the port.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
request_port(port)
|
|
Request any memory and IO region resources required by the port.
|
|
If any fail, no resources should be registered when this function
|
|
returns, and it should return -EBUSY on failure.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
config_port(port,type)
|
|
Perform any autoconfiguration steps required for the port. `type`
|
|
contains a bit mask of the required configuration. UART_CONFIG_TYPE
|
|
indicates that the port requires detection and identification.
|
|
port->type should be set to the type found, or PORT_UNKNOWN if
|
|
no port was detected.
|
|
|
|
UART_CONFIG_IRQ indicates autoconfiguration of the interrupt signal,
|
|
which should be probed using standard kernel autoprobing techniques.
|
|
This is not necessary on platforms where ports have interrupts
|
|
internally hard wired (eg, system on a chip implementations).
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
verify_port(port,serinfo)
|
|
Verify the new serial port information contained within serinfo is
|
|
suitable for this port type.
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
ioctl(port,cmd,arg)
|
|
Perform any port specific IOCTLs. IOCTL commands must be defined
|
|
using the standard numbering system found in <asm/ioctl.h>
|
|
|
|
Locking: none.
|
|
Interrupts: caller dependent.
|
|
|
|
Other functions
|
|
---------------
|
|
|
|
uart_update_timeout(port,cflag,quot)
|
|
Update the FIFO drain timeout, port->timeout, according to the
|
|
number of bits, parity, stop bits and quotient.
|
|
|
|
Locking: caller is expected to take port->lock
|
|
Interrupts: n/a
|
|
|
|
uart_get_baud_rate(port,termios)
|
|
Return the numeric baud rate for the specified termios, taking
|
|
account of the special 38400 baud "kludge". The B0 baud rate
|
|
is mapped to 9600 baud.
|
|
|
|
Locking: caller dependent.
|
|
Interrupts: n/a
|
|
|
|
uart_get_divisor(port,termios,oldtermios)
|
|
Return the divsor (baud_base / baud) for the selected baud rate
|
|
specified by termios. If the baud rate is out of range, try
|
|
the original baud rate specified by oldtermios (if non-NULL).
|
|
If that fails, try 9600 baud.
|
|
|
|
If 38400 baud and custom divisor is selected, return the
|
|
custom divisor instead.
|
|
|
|
Locking: caller dependent.
|
|
Interrupts: n/a
|
|
|
|
Other notes
|
|
-----------
|
|
|
|
It is intended some day to drop the 'unused' entries from uart_port, and
|
|
allow low level drivers to register their own individual uart_port's with
|
|
the core. This will allow drivers to use uart_port as a pointer to a
|
|
structure containing both the uart_port entry with their own extensions,
|
|
thus:
|
|
|
|
struct my_port {
|
|
struct uart_port port;
|
|
int my_stuff;
|
|
};
|