Linux-2.6.12-rc2

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!

1 files changed, 330 insertions, 0 deletions

diff --git a/Documentation/serial/driver b/Documentation/serial/driver
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+
+                        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;
+        };