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linux-next/Documentation/ABI/testing/sysfs-bus-intel_th-devices-msc
Alexander Shishkin 615c164da0 intel_th: msu: Introduce buffer interface
Introduces a concept of external buffers, which is a mechanism for creating
trace sinks that would receive trace data from MSC buffers and transfer it
elsewhere.

A external buffer can implement its own window allocation/deallocation if
it has to. It must provide a callback that's used to notify it when a
window fills up, so that it can then start a DMA transaction from that
window 'elsewhere'. This window remains in a 'locked' state and won't be
used for storing new trace data until the buffer 'unlocks' it with a
provided API call, at which point the window can be used again for storing
trace data.

This relies on a functional "last block" interrupt, so not all versions of
Trace Hub can use this feature, which does not reflect on existing users.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20190705141425.19894-2-alexander.shishkin@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-07-25 13:03:18 +02:00

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What: /sys/bus/intel_th/devices/<intel_th_id>-msc<msc-id>/wrap
Date: June 2015
KernelVersion: 4.3
Contact: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Description: (RW) Configure MSC buffer wrapping. 1 == wrapping enabled.
What: /sys/bus/intel_th/devices/<intel_th_id>-msc<msc-id>/mode
Date: June 2015
KernelVersion: 4.3
Contact: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Description: (RW) Configure MSC operating mode:
- "single", for contiguous buffer mode (high-order alloc);
- "multi", for multiblock mode;
- "ExI", for DCI handler mode;
- "debug", for debug mode;
- any of the currently loaded buffer sinks.
If operating mode changes, existing buffer is deallocated,
provided there are no active users and tracing is not enabled,
otherwise the write will fail.
What: /sys/bus/intel_th/devices/<intel_th_id>-msc<msc-id>/nr_pages
Date: June 2015
KernelVersion: 4.3
Contact: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Description: (RW) Configure MSC buffer size for "single" or "multi" modes.
In single mode, this is a single number of pages, has to be
power of 2. In multiblock mode, this is a comma-separated list
of numbers of pages for each window to be allocated. Number of
windows is not limited.
Writing to this file deallocates existing buffer (provided
there are no active users and tracing is not enabled) and then
allocates a new one.
What: /sys/bus/intel_th/devices/<intel_th_id>-msc<msc-id>/win_switch
Date: May 2019
KernelVersion: 5.2
Contact: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Description: (RW) Trigger window switch for the MSC's buffer, in
multi-window mode. In "multi" mode, accepts writes of "1", thereby
triggering a window switch for the buffer. Returns an error in any
other operating mode or attempts to write something other than "1".