[PATCH v3 0/3] can: length: fix definitions and add bit length calculation

From: Vincent Mailhol
Date: Tue May 30 2023 - 10:47:14 EST

When created in [1], frames length definitions were added to implement
byte queue limits (bql). Because bql expects lengths in bytes, bit
length definitions were not considered back then.

Recently, a need to refer to the exact frame length in bits, with CAN
bit stuffing, appeared in [2].

This series introduces can_frame_bits(): a function-like macro that
can calculate the exact size of a CAN(-FD) frame in bits with or
without bitsuffing.

[1] commit 85d99c3e2a13 ("can: length: can_skb_get_frame_len(): introduce
function to get data length of frame in data link layer")
Link: https://git.kernel.org/torvalds/c/85d99c3e2a13

[2] RE: [PATCH] can: mcp251xfd: Increase poll timeout
Link: https://lore.kernel.org/linux-can/BL3PR11MB64846C83ACD04E9330B0FE66FB729@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

* Changelog *

v2 -> v3:

* turn can_frame_bits() and can_frame_bytes() into function-like
macros. The fact that inline functions can not be used to
initialize constant structure fields was bothering me. I did my
best to make the macro look as less ugly as possible.

* as reported by Simon Horman, add missing document for the is_fd
argument of can_frame_bits().

Link: https://lore.kernel.org/linux-can/20230523065218.51227-1-mailhol.vincent@xxxxxxxxxx/

v1 -> v2:

* as suggested by Thomas Kopp, add a new patch to the series to fix
the stuff bit count and the fixed stuff bits definitions

* and another patch to fix documentation of the Remote Request
Substitution (RRS).

* refactor the length definition. Instead of using individual macro,
rely on an inline function. One reason is to minimize the number
of definitions. An other reason is that because the dynamic bit
stuff is calculated differently for CAN and CAN-FD, it is just not
possible to multiply the existing CANFD_FRAME_OVERHEAD_SFF/EFF by
the overhead ratio to get the bitsuffing: for CAN-FD, the CRC
field is already stuffed by the fix stuff bits and is out of scope
of the dynamic bitstuffing.

Link: https://lore.kernel.org/linux-can/20230507155506.3179711-1-mailhol.vincent@xxxxxxxxxx/

Vincent Mailhol (3):
can: length: fix bitstuffing count
can: length: fix description of the RRS field
can: length: refactor frame lengths definition to add size in bits

drivers/net/can/dev/length.c | 15 +-
include/linux/can/length.h | 295 +++++++++++++++++++++++++----------
2 files changed, 213 insertions(+), 97 deletions(-)