Re: [PATCH i2c-tools v2 0/2] Add support for message modifier flags

[Jean Delvare <jdelvare@suse.de>]

Hi Benoït, hi Wolfram,

On Tue, 23 Dec 2025 14:22:41 +0100, Benoît Monin wrote:
> I2C messages can be modified with a set of flags covered by the protocol
> mangling and the skip repeated start functionalities. This series add
> support for such flags to i2cdetect and i2ctransfer.
> 
> The first patch shows the support of protocol mangling and repeated
> start skipping in the output of 'i2cdetect -F'.
> 
> The second patch adds the parsing of optional flags to i2ctransfer
> message description. Those command-line flags then set the i2c message
> flags alongside the read/write flag.
> 
> I wrote these changes to test the insertion of I2C_M_STOP flag in
> multi-message transactions with i2ctransfer, but the other flags can be
> useful for various test scenarios.

Out of curiosity, did you have an actual scenario where you needed to
do this? Protocol mangling is supposed to be rarely needed and avoided
as much as possible.

> The patches use defines that have been present in the kernel since
> v3.6 released in 2012. If compatibility with older kernel is required,
> we will need to wrap some of them with #ifndef ... #endif.
> 
> Maybe a minimum kernel version can be documented in the README?

Be careful if you do. Kernel versions are a very broad indicator,
distribution kernel maintainers keep backporting features so an older
kernel can actually support something when its version suggests it
wouldn't. A kernel version should always be complemented with the actual
feature or flag so that users can look it up if needed.

> 
> Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
> ---
> Changes in v2:
> - Document the flags in i2ctransfer.8 man page.
> - Link to v1: https://lore.kernel.org/r/20251128-msg-flags-v1-0-6353f26fa6bc@bootlin.com
> 
> ---
> Benoît Monin (2):
>       i2cdetect: Display mangling and nostart support
>       i2ctransfer: Add optional message modifier flags
> 
>  tools/i2cdetect.c   |  4 ++++
>  tools/i2ctransfer.8 | 26 +++++++++++++++++++++++++-
>  tools/i2ctransfer.c | 34 +++++++++++++++++++++++++---------
>  3 files changed, 54 insertions(+), 10 deletions(-)
> ---
> base-commit: ea51da725b743da00b894dfdc4ab189f5a51e90e
> change-id: 20251127-msg-flags-3d2b2da9ae28

I have read Wolfram's review of your patch set (thanks Wolfram!) and
must say I agree with everything he wrote.

-- 
Jean Delvare
SUSE L3 Support