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linux-next/Documentation/ABI/testing/sysfs-tty
Yoshihiro YUNOMAE aef9a7bd9b serial/uart/8250: Add tunable RX interrupt trigger I/F of FIFO buffers
Add tunable RX interrupt trigger I/F of FIFO buffers.

Serial devices are used as not only message communication devices but control
or sending communication devices. For the latter uses, normally small data
will be exchanged, so user applications want to receive data unit as soon as
possible for real-time tendency. If we have a sensor which sends a 1 byte data
each time and must control a device based on the sensor feedback, the RX
interrupt should be triggered for each data.

According to HW specification of serial UART devices, RX interrupt trigger
can be changed, but the trigger is hard-coded. For example, RX interrupt trigger
in 16550A can be set to 1, 4, 8, or 14 bytes for HW, but current driver sets
the trigger to only 8bytes.

This patch makes some devices change RX interrupt trigger from userland.

<How to use>
- Read current setting
 # cat /sys/class/tty/ttyS0/rx_trig_bytes
 8

- Write user setting
 # echo 1 > /sys/class/tty/ttyS0/rx_trig_bytes
 # cat /sys/class/tty/ttyS0/rx_trig_bytes
 1

<Support uart devices>
- 16550A and Tegra (1, 4, 8, or 14 bytes)
- 16650V2 (8, 16, 24, or 28 bytes)
- 16654 (8, 16, 56, or 60 bytes)
- 16750 (1, 16, 32, or 56 bytes)

<Change log>
Changes in V9:
 - Use attr_group instead of dev_spec_attr_group of uart_port structure

Changes in V8:
 - Divide this patch from V7's patch based on Greg's comment

Changes in V7:
 - Add Documentation
 - Change I/F name from rx_int_trig to rx_trig_bytes because the name
   rx_int_trig is hard to understand how users specify the value

Changes in V6:
 - Move FCR_RX_TRIG_* definition in 8250.h to include/uapi/linux/serial_reg.h,
   rename those to UART_FCR_R_TRIG_*, and use UART_FCR_TRIGGER_MASK to
   UART_FCR_R_TRIG_BITS()
 - Change following function names:
    convert_fcr2val() => fcr_get_rxtrig_bytes()
    convert_val2rxtrig() => bytes_to_fcr_rxtrig()
 - Fix typo in serial8250_do_set_termios()
 - Delete the verbose error message pr_info() in bytes_to_fcr_rxtrig()
 - Rename *rx_int_trig/rx_trig* to *rxtrig* for several functions or variables
   (but UI remains rx_int_trig)
 - Change the meaningless variable name 'val' to 'bytes' following functions:
    fcr_get_rxtrig_bytes(), bytes_to_fcr_rxtrig(), do_set_rxtrig(),
    do_serial8250_set_rxtrig(), and serial8250_set_attr_rxtrig()
 - Use up->fcr in order to get rxtrig_bytes instead of rx_trig_raw in
   fcr_get_rxtrig_bytes()
 - Use conf_type->rxtrig_bytes[0] instead of switch statement for support check
   in register_dev_spec_attr_grp()
 - Delete the checking whether a user changed FCR or not when minimum buffer
   is needed in serial8250_do_set_termios()

Changes in V5.1:
 - Fix FCR_RX_TRIG_MAX_STATE definition

Changes in V5:
 - Support Tegra, 16650V2, 16654, and 16750
 - Store default FCR value to up->fcr when the port is first created
 - Add rx_trig_byte[] in uart_config[] for each device and use rx_trig_byte[]
   in convert_fcr2val() and convert_val2rxtrig()

Changes in V4:
 - Introduce fifo_bug flag in uart_8250_port structure
   This is enabled only when parity is enabled and UART_BUG_PARITY is enabled
   for up->bugs. If this flag is enabled, user cannot set RX trigger.
 - Return -EOPNOTSUPP when it does not support device at convert_fcr2val() and
   at convert_val2rxtrig()
 - Set the nearest lower RX trigger when users input a meaningless value at
   convert_val2rxtrig()
 - Check whether p->fcr is existing at serial8250_clear_and_reinit_fifos()
 - Set fcr = up->fcr in the begging of serial8250_do_set_termios()

Changes in V3:
 - Change I/F from ioctl(2) to sysfs(rx_int_trig)

Changed in V2:
 - Use _IOW for TIOCSFIFORTRIG definition
 - Pass the interrupt trigger value itself

Signed-off-by: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-07-17 18:23:35 -07:00

157 lines
4.7 KiB
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What: /sys/class/tty/console/active
Date: Nov 2010
Contact: Kay Sievers <kay.sievers@vrfy.org>
Description:
Shows the list of currently configured
console devices, like 'tty1 ttyS0'.
The last entry in the file is the active
device connected to /dev/console.
The file supports poll() to detect virtual
console switches.
What: /sys/class/tty/tty0/active
Date: Nov 2010
Contact: Kay Sievers <kay.sievers@vrfy.org>
Description:
Shows the currently active virtual console
device, like 'tty1'.
The file supports poll() to detect virtual
console switches.
What: /sys/class/tty/ttyS0/uartclk
Date: Sep 2012
Contact: Tomas Hlavacek <tmshlvck@gmail.com>
Description:
Shows the current uartclk value associated with the
UART port in serial_core, that is bound to TTY like ttyS0.
uartclk = 16 * baud_base
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/type
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Shows the current tty type for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/line
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Shows the current tty line number for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/port
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Shows the current tty port I/O address for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/irq
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Shows the current primary interrupt for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/flags
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the tty port status flags for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/xmit_fifo_size
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the transmit FIFO size for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/close_delay
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the closing delay time for this port in ms.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/closing_wait
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the close wait time for this port in ms.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/custom_divisor
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the custom divisor if any that is set on this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/io_type
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the I/O type that is to be used with the iomem base
address.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/iomem_base
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
The I/O memory base for this port.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/iomem_reg_shift
Date: October 2012
Contact: Alan Cox <alan@linux.intel.com>
Description:
Show the register shift indicating the spacing to be used
for accesses on this iomem address.
These sysfs values expose the TIOCGSERIAL interface via
sysfs rather than via ioctls.
What: /sys/class/tty/ttyS0/rx_trig_bytes
Date: May 2014
Contact: Yoshihiro YUNOMAE <yoshihiro.yunomae.ez@hitachi.com>
Description:
Shows current RX interrupt trigger bytes or sets the
user specified value to change it for the FIFO buffer.
Users can show or set this value regardless of opening the
serial device file or not.
The RX trigger can be set one of four kinds of values for UART
serials. When users input a meaning less value to this I/F,
the RX trigger is changed to the nearest lower value for the
device specification. For example, when user sets 7bytes on
16550A, which has 1/4/8/14 bytes trigger, the RX trigger is
automatically changed to 4 bytes.