>>>> Implement a UART register tracing facility using the debugfs. This can be
>>>> used as a "serial port sniffer" to monitor UART traffic and line settings
>>>> with timestamps at microsecond granularity. This can be useful for general
>>>> serial port debugging or to debug the UART driver itself.
>>>
>>>> drivers/tty/serial/8250/8250_debug.c | 530 +++++++++++++++++++++++++++
>>>
>>> My gosh. Why trace points and trace events can't be used for that?
>>
>> I don't understand your post. Are you saying there is already a way to
>> trace UART register reads/writes without this patch? Can you elaborate?
>
> Besides what Greg an I were telling you (another type of infrastructure),
> as a matter of fact you may trace any IO on some architectures (at least x86),
> it's called mmiotracer (I have used it like 5 years ago or so to trace UART).
>
> Below is the excerpt from my old shell script
>
> rebind() {
> local drvdir="/sys/bus/$1/drivers/$2"
> local devdir="/sys/bus/$1/devices/$3"
> [ -d "$drvdir" -a -d "$devdir" ] || return
> echo "$3" > "$drvdir/unbind"
> echo "$3" > "$drvdir/bind"
> }
>
> mmiotrace() {
> echo mmiotrace > /sys/kernel/tracing/current_tracer
> echo 1 > /sys/kernel/tracing/tracing_on
>
> rebind platform 'dw-apb-uart' '80860F0A:00' # BYT ttyS1 (ACPI)
> rebind platform 'dw-apb-uart' '8086228A:00' # BSW ttyS1 (ACPI)
> rebind pci '8250_mid' '0000:00:04.2' # Edison ttyS1
> rebind pci 'intel-lpss' '0000:00:18.1' # BXT LH ttyS1
> rebind pci 'intel-lpss' '0000:00:1e.0' # SKL ttyS1
> rebind pci '8250_lpss' '0000:00:1e.3' # BSW ttyS1 (PCI)
> }
Correct me if I'm wrong but I don't think mmiotrace will work for me. My
environment comprises an Intel Celeron M connected to an 852GM north bridge,
an ICH4 south bridge, and a SCH3114 Super I/O controller. My UART device
is ttyS1 and it uses port I/O not memory-mapped I/O.
# find /sys/devices -name '*ttyS*'
/sys/devices/platform/serial8250/tty/ttyS2
/sys/devices/platform/serial8250/tty/ttyS3
/sys/devices/pnp0/00:03/tty/ttyS0
/sys/devices/pnp0/00:04/tty/ttyS1
# ls -l /sys/bus/pnp/drivers/serial
total 0
lrwxrwxrwx 1 root root 0 Sep 11 14:19 00:03 -> ../../../../devices/pnp0/00:03
lrwxrwxrwx 1 root root 0 Sep 11 14:19 00:04 -> ../../../../devices/pnp0/00:04
--w------- 1 root root 4096 Sep 11 14:19 bind
--w------- 1 root root 4096 Sep 11 14:19 uevent
--w------- 1 root root 4096 Sep 11 14:19 unbind
# mount -t tracefs tracefs /sys/kernel/tracing
# echo mmiotrace > /sys/kernel/tracing/current_tracer
# echo 00:04 > /sys/bus/pnp/drivers/serial/unbind
# echo 00:04 > /sys/bus/pnp/drivers/serial/bind
# dmesg | tail -5
[ 36.438305] random: crng init done
[ 97.736362] mmiotrace: enabled.
[ 113.964953] serial 00:04: disabled
[ 117.469704] serial 00:04: activated
[ 117.469986] 00:04: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A
(perform UART transaction)
# cat /sys/kernel/tracing/trace
# tracer: mmiotrace
#
# entries-in-buffer/entries-written: 0/0 #P:1
#
# _-----=> irqs-off/BH-disabled
# / _----=> need-resched
# | / _---=> hardirq/softirq
# || / _--=> preempt-depth
# ||| / _-=> migrate-disable
# |||| / delay
# TASK-PID CPU# ||||| TIMESTAMP FUNCTION
# | | | ||||| | |
