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- In-kernel memory-mapped I/O tracing
-
-
-Home page and links to optional user space tools:
-
- http://nouveau.freedesktop.org/wiki/MmioTrace
-
-MMIO tracing was originally developed by Intel around 2003 for their Fault
-Injection Test Harness. In Dec 2006 - Jan 2007, using the code from Intel,
-Jeff Muizelaar created a tool for tracing MMIO accesses with the Nouveau
-project in mind. Since then many people have contributed.
-
-Mmiotrace was built for reverse engineering any memory-mapped IO device with
-the Nouveau project as the first real user. Only x86 and x86_64 architectures
-are supported.
-
-Out-of-tree mmiotrace was originally modified for mainline inclusion and
-ftrace framework by Pekka Paalanen <pq@iki.fi>.
-
-
-Preparation
------------
-
-Mmiotrace feature is compiled in by the CONFIG_MMIOTRACE option. Tracing is
-disabled by default, so it is safe to have this set to yes. SMP systems are
-supported, but tracing is unreliable and may miss events if more than one CPU
-is on-line, therefore mmiotrace takes all but one CPU off-line during run-time
-activation. You can re-enable CPUs by hand, but you have been warned, there
-is no way to automatically detect if you are losing events due to CPUs racing.
-
-
-Usage Quick Reference
----------------------
-
-$ mount -t debugfs debugfs /sys/kernel/debug
-$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
-$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
-Start X or whatever.
-$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
-$ echo nop > /sys/kernel/debug/tracing/current_tracer
-Check for lost events.
-
-
-Usage
------
-
-Make sure debugfs is mounted to /sys/kernel/debug.
-If not (requires root privileges):
-$ mount -t debugfs debugfs /sys/kernel/debug
-
-Check that the driver you are about to trace is not loaded.
-
-Activate mmiotrace (requires root privileges):
-$ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
-
-Start storing the trace:
-$ cat /sys/kernel/debug/tracing/trace_pipe > mydump.txt &
-The 'cat' process should stay running (sleeping) in the background.
-
-Load the driver you want to trace and use it. Mmiotrace will only catch MMIO
-accesses to areas that are ioremapped while mmiotrace is active.
-
-During tracing you can place comments (markers) into the trace by
-$ echo "X is up" > /sys/kernel/debug/tracing/trace_marker
-This makes it easier to see which part of the (huge) trace corresponds to
-which action. It is recommended to place descriptive markers about what you
-do.
-
-Shut down mmiotrace (requires root privileges):
-$ echo nop > /sys/kernel/debug/tracing/current_tracer
-The 'cat' process exits. If it does not, kill it by issuing 'fg' command and
-pressing ctrl+c.
-
-Check that mmiotrace did not lose events due to a buffer filling up. Either
-$ grep -i lost mydump.txt
-which tells you exactly how many events were lost, or use
-$ dmesg
-to view your kernel log and look for "mmiotrace has lost events" warning. If
-events were lost, the trace is incomplete. You should enlarge the buffers and
-try again. Buffers are enlarged by first seeing how large the current buffers
-are:
-$ cat /sys/kernel/debug/tracing/buffer_size_kb
-gives you a number. Approximately double this number and write it back, for
-instance:
-$ echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
-Then start again from the top.
-
-If you are doing a trace for a driver project, e.g. Nouveau, you should also
-do the following before sending your results:
-$ lspci -vvv > lspci.txt
-$ dmesg > dmesg.txt
-$ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt
-and then send the .tar.gz file. The trace compresses considerably. Replace
-"pciid" and "nick" with the PCI ID or model name of your piece of hardware
-under investigation and your nickname.
-
-
-How Mmiotrace Works
--------------------
-
-Access to hardware IO-memory is gained by mapping addresses from PCI bus by
-calling one of the ioremap_*() functions. Mmiotrace is hooked into the
-__ioremap() function and gets called whenever a mapping is created. Mapping is
-an event that is recorded into the trace log. Note that ISA range mappings
-are not caught, since the mapping always exists and is returned directly.
-
-MMIO accesses are recorded via page faults. Just before __ioremap() returns,
-the mapped pages are marked as not present. Any access to the pages causes a
-fault. The page fault handler calls mmiotrace to handle the fault. Mmiotrace
-marks the page present, sets TF flag to achieve single stepping and exits the
-fault handler. The instruction that faulted is executed and debug trap is
-entered. Here mmiotrace again marks the page as not present. The instruction
-is decoded to get the type of operation (read/write), data width and the value
-read or written. These are stored to the trace log.
-
-Setting the page present in the page fault handler has a race condition on SMP
-machines. During the single stepping other CPUs may run freely on that page
-and events can be missed without a notice. Re-enabling other CPUs during
-tracing is discouraged.
-
-
-Trace Log Format
-----------------
-
-The raw log is text and easily filtered with e.g. grep and awk. One record is
-one line in the log. A record starts with a keyword, followed by keyword-
-dependent arguments. Arguments are separated by a space, or continue until the
-end of line. The format for version 20070824 is as follows:
-
-Explanation Keyword Space-separated arguments
----------------------------------------------------------------------------
-
-read event R width, timestamp, map id, physical, value, PC, PID
-write event W width, timestamp, map id, physical, value, PC, PID
-ioremap event MAP timestamp, map id, physical, virtual, length, PC, PID
-iounmap event UNMAP timestamp, map id, PC, PID
-marker MARK timestamp, text
-version VERSION the string "20070824"
-info for reader LSPCI one line from lspci -v
-PCI address map PCIDEV space-separated /proc/bus/pci/devices data
-unk. opcode UNKNOWN timestamp, map id, physical, data, PC, PID
-
-Timestamp is in seconds with decimals. Physical is a PCI bus address, virtual
-is a kernel virtual address. Width is the data width in bytes and value is the
-data value. Map id is an arbitrary id number identifying the mapping that was
-used in an operation. PC is the program counter and PID is process id. PC is
-zero if it is not recorded. PID is always zero as tracing MMIO accesses
-originating in user space memory is not yet supported.
-
-For instance, the following awk filter will pass all 32-bit writes that target
-physical addresses in the range [0xfb73ce40, 0xfb800000[
-
-$ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 &&
-adr < 0xfb800000) print; }'
-
-
-Tools for Developers
---------------------
-
-The user space tools include utilities for:
-- replacing numeric addresses and values with hardware register names
-- replaying MMIO logs, i.e., re-executing the recorded writes
-
-