Merge branch 'lib-packing-introduce-and-use-un-pack_fields'

Jacob Keller says:

====================
lib: packing: introduce and use (un)pack_fields

This series improves the packing library with a new API for packing or
unpacking a large number of fields at once with minimal code footprint. The
API is then used to replace bespoke packing logic in the ice driver,
preparing it to handle unpacking in the future. Finally, the ice driver has
a few other cleanups related to the packing logic.

The pack_fields and unpack_fields functions have the following improvements
over the existing pack() and unpack() API:

 1. Packing or unpacking a large number of fields takes significantly less
    code. This significantly reduces the .text size for an increase in the
    .data size which is much smaller.

 2. The unpacked data can be stored in sizes smaller than u64 variables.
    This reduces the storage requirement both for runtime data structures,
    and for the rodata defining the fields. This scales with the number of
    fields used.

 3. Most of the error checking is done at compile time, rather than
    runtime, via CHECK_PACKED_FIELD macros.

The actual packing and unpacking code still uses the u64 size
variables. However, these are converted to the appropriate field sizes when
storing or reading the data from the buffer.

This version now uses significantly improved macro checks, thanks to the
work of Vladimir. We now only need 300 lines of macro for the generated
checks. In addition, each new check only requires 4 lines of code for its
macro implementation and 1 extra line in the CHECK_PACKED_FIELDS macro.
This is significantly better than previous versions which required ~2700
lines.

The CHECK_PACKED_FIELDS macro uses __builtin_choose_expr to select the
appropriately sized CHECK_PACKED_FIELDS_N macro. This enables directly
adding CHECK_PACKED_FIELDS calls into the pack_fields and unpack_fields
macros. Drivers no longer need to call the CHECK_PACKED_FIELDS_N macros
directly, and we do not need to modify Kbuild or introduce multiple CONFIG
options.

The code for the CHECK_PACKED_FIELDS_(0..50) and CHECK_PACKED_FIELDS itself
can be generated from the C program in scripts/gen_packed_field_checks.c.
This little C program may be used in the future to update the checks to
more sizes if a driver with more than 50 fields appears in the future.
The total amount of required code is now much smaller, and we don't
anticipate needing to increase the size very often. Thus, it makes sense to
simply commit the result directly instead of attempting to modify Kbuild to
automatically generate it.

This version uses the 5-argument format of pack_fields and unpack_fields,
with the size of the packed buffer passed as one of the arguments. We do
enforce that the compiler can tell its a constant using
__builtin_constant_p(), ensuring that the size checks are handled at
compile time. We could reduce these to 4 arguments and require that the
passed in pbuf be of a type which has the appropriate size. I opted against
that because it makes the API less flexible and a bit less natural to use
in existing code.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
v9: https://lore.kernel.org/20241204-packing-pack-fields-and-ice-implementation-v9-0-81c8f2bd7323@intel.com
v8: https://lore.kernel.org/20241203-packing-pack-fields-and-ice-implementation-v8-0-2ed68edfe583@intel.com
v7: https://lore.kernel.org/20241202-packing-pack-fields-and-ice-implementation-v7-0-ed22e38e6c65@intel.com
v6: https://lore.kernel.org/20241118-packing-pack-fields-and-ice-implementation-v6-0-6af8b658a6c3@intel.com
v5: https://lore.kernel.org/20241111-packing-pack-fields-and-ice-implementation-v5-0-80c07349e6b7@intel.com
v4: https://lore.kernel.org/20241108-packing-pack-fields-and-ice-implementation-v4-0-81a9f42c30e5@intel.com
v3: https://lore.kernel.org/20241107-packing-pack-fields-and-ice-implementation-v3-0-27c566ac2436@intel.com
v2: https://lore.kernel.org/20241025-packing-pack-fields-and-ice-implementation-v2-0-734776c88e40@intel.com
v1: https://lore.kernel.org/20241011-packing-pack-fields-and-ice-implementation-v1-0-d9b1f7500740@intel.com
====================

Link: https://patch.msgid.link/20241210-packing-pack-fields-and-ice-implementation-v10-0-ee56a47479ac@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>