Re: [PATCH v4 3/3] i3c: add i3cdev module to expose i3c dev in /dev

[Sam Agazaryan]

> actual_len is a problem.  Only 2 controller drivers support it.
> No I3C device drivers support it.  mctp-i3c reads len not actual_len.
> regmap-i3c ignores len and actual_len.  And its definition comment
> is not exactly correct since it is only valid for reads.
>
> Despite that, the additional issue here, is what to do about a short
> read.  Seems like it should be in the uapi, but actual_len needs to
> be fixed first.

I think something we can do to get around this is to incorporate one
of Meagan's patches
[1] which addresses actual_len usage in all the controller drivers.

With controller support we can add a field for actual_len in the UAPI struct:

    struct i3c_ioc_xfer {
        __u64 data;
        __u16 len;
        __u16 actual_len;
        union {
            __u8 rnw;
            __u8 cmd;
        };
        __u8 mode;
        __u8 pad[2];
    };

As a follow up, I can also help clean up other i3c drivers in future
changes, such as mctp-i3c
since at that point we should have actual_len support across all the
controller drivers.

Thanks,
Sam

[1] https://lore.kernel.org/r/20260911210935.1353126-3-meaganlloyd@xxxxxxxxxxxxxxxxxxx