Jacob Keller has a use case for packing() in the intel/ice networking
driver, but it cannot be used as-is.
Simply put, the API quirks for LSW32_IS_FIRST and LITTLE_ENDIAN are
naively implemented with the undocumented assumption that the buffer
length must be a multiple of 4. All calculations of group offsets and
offsets of bytes within groups assume that this is the case. But in the
ice case, this does not hold true. For example, packing into a buffer
of 22 bytes would yield wrong results, but pretending it was a 24 byte
buffer would work.
Rather than requiring such hacks, and leaving a big question mark when
it comes to discontinuities in the accessible bit fields of such buffer,
we should extend the packing API to support this use case.
It turns out that we can keep the design in terms of groups of 4 bytes,
but also make it work if the total length is not a multiple of 4.
Just like before, imagine the buffer as a big number, and its most
significant bytes (the ones that would make up to a multiple of 4) are
missing. Thus, with a big endian (no quirks) interpretation of the
buffer, those most significant bytes would be absent from the beginning
of the buffer, and with a LSW32_IS_FIRST interpretation, they would be
absent from the end of the buffer. The LITTLE_ENDIAN quirk, in the
packing() API world, only affects byte ordering within groups of 4.
Thus, it does not change which bytes are missing. Only the significance
of the remaining bytes within the (smaller) group.
No change intended for buffer sizes which are multiples of 4. Tested
with the sja1105 driver and with downstream unit tests.
Link: https://lore.kernel.org/netdev/a0338310-e66c-497c-bc1f-a597e50aa3ff@intel.com/
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20241002-packing-kunit-tests-and-split-pack-unpack-v2-2-8373e551eae3@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Correct spelling problems for Documentation/core-api/packing.rst as
reported by codespell.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vladimir Oltean <olteanv@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Link: https://lore.kernel.org/r/20230215053738.11562-1-rdunlap@infradead.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
The packing.txt file was misplaced, as docs should be part of
a documentation book, and not at the root dir.
So, move it to the core-api directory and add to its index.
Also, ensure that the file will be properly parsed and the bitmap
ascii artwork will use a monotonic font.
Fixes: 554aae3500 ("lib: Add support for generic packing operations")
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
