Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 184 insertions, 0 deletions

diff --git a/Documentation/trace/mmiotrace.rst b/Documentation/trace/mmiotrace.rst
new file mode 100644
index 000000000..5116e8ca2
--- /dev/null
+++ b/Documentation/trace/mmiotrace.rst
@@ -0,0 +1,184 @@
+===================================
+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
+
+