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Intel(R) Trace Hub (TH) is a set of hardware blocks (subdevices) that produce, switch and output trace data from multiple hardware and software sources over several types of trace output ports encoded in System Trace Protocol (MIPI STPv2) and is intended to perform full system debugging. For these subdevices, we create a bus, where they can be discovered and configured by userspace software. This patch creates this bus infrastructure, three types of devices (source, output, switch), resource allocation, some callback mechanisms to facilitate communication between the subdevices' drivers and some common sysfs attributes. Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
Intel(R) Trace Hub (TH)
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=======================
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Overview
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--------
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Intel(R) Trace Hub (TH) is a set of hardware blocks that produce,
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switch and output trace data from multiple hardware and software
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sources over several types of trace output ports encoded in System
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Trace Protocol (MIPI STPv2) and is intended to perform full system
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debugging. For more information on the hardware, see Intel(R) Trace
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Hub developer's manual [1].
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It consists of trace sources, trace destinations (outputs) and a
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switch (Global Trace Hub, GTH). These devices are placed on a bus of
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their own ("intel_th"), where they can be discovered and configured
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via sysfs attributes.
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Currently, the following Intel TH subdevices (blocks) are supported:
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- Software Trace Hub (STH), trace source, which is a System Trace
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Module (STM) device,
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- Memory Storage Unit (MSU), trace output, which allows storing
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trace hub output in system memory,
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- Parallel Trace Interface output (PTI), trace output to an external
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debug host via a PTI port,
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- Global Trace Hub (GTH), which is a switch and a central component
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of Intel(R) Trace Hub architecture.
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Common attributes for output devices are described in
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Documentation/ABI/testing/sysfs-bus-intel_th-output-devices, the most
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notable of them is "active", which enables or disables trace output
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into that particular output device.
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GTH allows directing different STP masters into different output ports
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via its "masters" attribute group. More detailed GTH interface
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description is at Documentation/ABI/testing/sysfs-bus-intel_th-devices-gth.
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STH registers an stm class device, through which it provides interface
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to userspace and kernelspace software trace sources. See
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Documentation/tracing/stm.txt for more information on that.
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MSU can be configured to collect trace data into a system memory
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buffer, which can later on be read from its device nodes via read() or
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mmap() interface.
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On the whole, Intel(R) Trace Hub does not require any special
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userspace software to function; everything can be configured, started
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and collected via sysfs attributes, and device nodes.
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[1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf
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Bus and Subdevices
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------------------
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For each Intel TH device in the system a bus of its own is
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created and assigned an id number that reflects the order in which TH
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devices were emumerated. All TH subdevices (devices on intel_th bus)
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begin with this id: 0-gth, 0-msc0, 0-msc1, 0-pti, 0-sth, which is
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followed by device's name and an optional index.
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Output devices also get a device node in /dev/intel_thN, where N is
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the Intel TH device id. For example, MSU's memory buffers, when
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allocated, are accessible via /dev/intel_th0/msc{0,1}.
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Quick example
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-------------
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# figure out which GTH port is the first memory controller:
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$ cat /sys/bus/intel_th/devices/0-msc0/port
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0
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# looks like it's port 0, configure master 33 to send data to port 0:
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$ echo 0 > /sys/bus/intel_th/devices/0-gth/masters/33
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# allocate a 2-windowed multiblock buffer on the first memory
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# controller, each with 64 pages:
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$ echo multi > /sys/bus/intel_th/devices/0-msc0/mode
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$ echo 64,64 > /sys/bus/intel_th/devices/0-msc0/nr_pages
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# enable wrapping for this controller, too:
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$ echo 1 > /sys/bus/intel_th/devices/0-msc0/wrap
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# and enable tracing into this port:
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$ echo 1 > /sys/bus/intel_th/devices/0-msc0/active
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# .. send data to master 33, see stm.txt for more details ..
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# .. wait for traces to pile up ..
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# .. and stop the trace:
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$ echo 0 > /sys/bus/intel_th/devices/0-msc0/active
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# and now you can collect the trace from the device node:
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$ cat /dev/intel_th0/msc0 > my_stp_trace
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