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

[Adrian Hunter <adrian.hunter@intel.com>]

On 15/09/2026 02:46, Sam Agazaryan wrote:
>> 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.

It is less confusing if it is all fixed up in one patch.  Fix the
comment on actual_len.  Make all controller drivers use actual_len
not len for returning the length of data read.  And fix up mctp-i3c too.

> 
> Thanks,
> Sam
> 
> [1] https://lore.kernel.org/r/20260911210935.1353126-3-meaganlloyd@linux.microsoft.com