mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-12 13:55:32 +00:00
![Jiri Slaby](/assets/img/avatar_default.png)
Group the flow flags under a single struct called flow. The new struct
contains 'stopped' and 'tco_stopped' bools which used to be bits in a
bitfield. The struct also contains the lock protecting them to
potentially share the same cache line.
Note that commit c545b66c69
(tty: Serialize tcflow() with other tty
flow control changes) added a padding to the original bitfield. It was
for the bitfield to occupy a whole 64b word to avoid interferring stores
on Alpha (cannot we evaporate this arch with weird implications to C
code yet?). But it doesn't work as expected as the padding
(tty_struct::unused) is aligned to a 8B boundary too and occupies some
bytes from the next word.
So make it reliable by:
1) setting __aligned of the struct -- that aligns the start, and
2) making 'unsigned long unused[0]' as the last member of the struct --
pads the end.
This is also the perfect time to start the documentation of tty_struct
where all this lives. So we start by documenting what these bools
actually serve for. And why we do all the alignment dances. Only the few
up-to-date information from the Theodore's comment made it into this new
Kerneldoc comment.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/20210505091928.22010-13-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
138 lines
4.1 KiB
ReStructuredText
138 lines
4.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
.. include:: <isonum.txt>
|
|
|
|
|
|
================
|
|
Using Linux CAIF
|
|
================
|
|
|
|
|
|
:Copyright: |copy| ST-Ericsson AB 2010
|
|
|
|
:Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
|
|
|
|
Start
|
|
=====
|
|
|
|
If you have compiled CAIF for modules do::
|
|
|
|
$modprobe crc_ccitt
|
|
$modprobe caif
|
|
$modprobe caif_socket
|
|
$modprobe chnl_net
|
|
|
|
|
|
Preparing the setup with a STE modem
|
|
====================================
|
|
|
|
If you are working on integration of CAIF you should make sure
|
|
that the kernel is built with module support.
|
|
|
|
There are some things that need to be tweaked to get the host TTY correctly
|
|
set up to talk to the modem.
|
|
Since the CAIF stack is running in the kernel and we want to use the existing
|
|
TTY, we are installing our physical serial driver as a line discipline above
|
|
the TTY device.
|
|
|
|
To achieve this we need to install the N_CAIF ldisc from user space.
|
|
The benefit is that we can hook up to any TTY.
|
|
|
|
The use of Start-of-frame-extension (STX) must also be set as
|
|
module parameter "ser_use_stx".
|
|
|
|
Normally Frame Checksum is always used on UART, but this is also provided as a
|
|
module parameter "ser_use_fcs".
|
|
|
|
::
|
|
|
|
$ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes
|
|
$ ifconfig caif_ttyS0 up
|
|
|
|
PLEASE NOTE:
|
|
There is a limitation in Android shell.
|
|
It only accepts one argument to insmod/modprobe!
|
|
|
|
Trouble shooting
|
|
================
|
|
|
|
There are debugfs parameters provided for serial communication.
|
|
/sys/kernel/debug/caif_serial/<tty-name>/
|
|
|
|
* ser_state: Prints the bit-mask status where
|
|
|
|
- 0x02 means SENDING, this is a transient state.
|
|
- 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent
|
|
and is blocking further send operation. Flow OFF has been propagated
|
|
to all CAIF Channels using this TTY.
|
|
|
|
* tty_status: Prints the bit-mask tty status information
|
|
|
|
- 0x01 - tty->warned is on.
|
|
- 0x04 - tty->packed is on.
|
|
- 0x08 - tty->flow.tco_stopped is on.
|
|
- 0x10 - tty->hw_stopped is on.
|
|
- 0x20 - tty->flow.stopped is on.
|
|
|
|
* last_tx_msg: Binary blob Prints the last transmitted frame.
|
|
|
|
This can be printed with::
|
|
|
|
$od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg.
|
|
|
|
The first two tx messages sent look like this. Note: The initial
|
|
byte 02 is start of frame extension (STX) used for re-syncing
|
|
upon errors.
|
|
|
|
- Enumeration::
|
|
|
|
0000000 02 05 00 00 03 01 d2 02
|
|
| | | | | |
|
|
STX(1) | | | |
|
|
Length(2)| | |
|
|
Control Channel(1)
|
|
Command:Enumeration(1)
|
|
Link-ID(1)
|
|
Checksum(2)
|
|
|
|
- Channel Setup::
|
|
|
|
0000000 02 07 00 00 00 21 a1 00 48 df
|
|
| | | | | | | |
|
|
STX(1) | | | | | |
|
|
Length(2)| | | | |
|
|
Control Channel(1)
|
|
Command:Channel Setup(1)
|
|
Channel Type(1)
|
|
Priority and Link-ID(1)
|
|
Endpoint(1)
|
|
Checksum(2)
|
|
|
|
* last_rx_msg: Prints the last transmitted frame.
|
|
|
|
The RX messages for LinkSetup look almost identical but they have the
|
|
bit 0x20 set in the command bit, and Channel Setup has added one byte
|
|
before Checksum containing Channel ID.
|
|
|
|
NOTE:
|
|
Several CAIF Messages might be concatenated. The maximum debug
|
|
buffer size is 128 bytes.
|
|
|
|
Error Scenarios
|
|
===============
|
|
|
|
- last_tx_msg contains channel setup message and last_rx_msg is empty ->
|
|
The host seems to be able to send over the UART, at least the CAIF ldisc get
|
|
notified that sending is completed.
|
|
|
|
- last_tx_msg contains enumeration message and last_rx_msg is empty ->
|
|
The host is not able to send the message from UART, the tty has not been
|
|
able to complete the transmit operation.
|
|
|
|
- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there
|
|
might be problems transmitting over UART.
|
|
|
|
E.g. host and modem wiring is not correct you will typically see
|
|
tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT).
|
|
|
|
You will probably see the enumeration message in last_tx_message
|
|
and empty last_rx_message.
|