doc: clarify usage of HARQ in bbdev
New paragraph is added for detailing typical VRAN usecase and mapping to bbdev API usage. Signed-off-by: Nicolas Chautru <nicolas.chautru@intel.com> Reviewed-by: Tom Rix <trix@redhat.com>
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@ -1054,6 +1054,37 @@ capability RTE_BBDEV_LDPC_INTERNAL_HARQ_MEMORY_OUT_ENABLE is set
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then the HARQ is stored in memory internal to the device and not visible
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to BBDEV.
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.. note::
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More explicitly for a typical usage of HARQ retransmission
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in a VRAN application using a HW PMD, there will be 2 cases.
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For 1st transmission, only the HARQ output is enabled:
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- the harq_combined_output.offset is provided to a given address.
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ie. typically an integer index * 32K,
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where the index is tracked by the application based on code block index
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for a given UE and HARQ process.
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- the related operation flag would notably include
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RTE_BBDEV_LDPC_HQ_COMBINE_OUT_ENABLE and RTE_BBDEV_LDPC_HARQ_6BIT_COMPRESSION.
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- note that no explicit flush or reset of the memory is required.
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For 2nd transmission, an input is also required to benefit from HARQ combination gain:
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- the changes mentioned above are the same (note that rvIndex may be adjusted).
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- the operation flag would additionally include the LDPC_HQ_COMBINE_IN_ENABLE flag.
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- the harq_combined_input.offset must be set to the address of the related code block
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(ie. same as the harq_combine_output index above for the same code block, HARQ process, UE).
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- the harq_combined_input.length must be set to the length
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which was provided back in the related harq_combined_output.length
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when it has processed and dequeued (previous HARQ iteration).
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The output mbuf data structures are expected to be allocated by the
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application with enough room for the output data.
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