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Gerhard Engleder says: ==================== ptp: Support hardware clocks with additional free running cycle counter ptp vclocks require a clock with free running time for the timecounter. Currently only a physical clock forced to free running is supported. If vclocks are used, then the physical clock cannot be synchronized anymore. The synchronized time is not available in hardware in this case. As a result, timed transmission with TAPRIO hardware support is not possible anymore. If hardware would support a free running time additionally to the physical clock, then the physical clock does not need to be forced to free running. Thus, the physical clocks can still be synchronized while vclocks are in use. The physical clock could be used to synchronize the time domain of the TSN network and trigger TAPRIO. In parallel vclocks can be used to synchronize other time domains. One year ago I thought for two time domains within a TSN network also two physical clocks are required. This would lead to new kernel interfaces for asking for the second clock, ... . But actually for a time triggered system like TSN there can be only one time domain that controls the system itself. All other time domains belong to other layers, but not to the time triggered system itself. So other time domains can be based on a free running counter if similar mechanisms like 2 step synchroisation are used. Synchronisation was tested with two time domains between two directly connected hosts. Each host run two ptp4l instances, the first used the physical clock and the second used the virtual clock. I used my FPGA based network controller as network device. ptp4l was used in combination with the virtual clock support patches from Miroslav Lichvar. v4: - if_index of 0 is invalid (Jonathan Lemon) - set if_index to 0 in the SOF_TIMESTAMPING_RAW_HARDWARE block (Jonathan Lemon) - add helper function for netdev_get_tstamp() call (Jonathan Lemon) - update SKBTX_ANY_TSTAMP (Paolo Abeni) - use separate bits for new tx_flags (Richard Cochran) v3: - optimize ptp_convert_timestamp (Richard Cochran) - call dev_get_by_napi_id() only if needed (Richard Cochran) - use non-negated logical test (Richard Cochran) - add comment for skipped output (Richard Cochran) - add comment for SKBTX_HW_TSTAMP_USE_CYCLES masking (Richard Cochran) v2: - rename ptp_clock cycles to has_cycles (Richard Cochran) - call it free running cycle counter (Richard Cochran) - update struct skb_shared_hwtstamps kdoc (Richard Cochran) - optimize timestamp address/cookie processing path (Richard Cochran, Vinicius Costa Gomes) v1: - complete rework based on suggestions (Richard Cochran) ==================== Link: https://lore.kernel.org/r/20220506200142.3329-1-gerhard@engleder-embedded.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.