On Thu, Aug 31, 2023 at 12:33:33PM -0600, Dan Raymond wrote:
> On 8/31/2023 12:08 PM, Andy Shevchenko wrote:
> > Warning: This email is from an unusual correspondent.
> > Warning: Make sure this is someone you trust.
> >
> > On Thu, Aug 24, 2023 at 02:59:01PM -0600, Dan Raymond wrote:
> >> 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)
}
--
With Best Regards,
Andy Shevchenko
