Apologies for chiming in this late ... I only got a chance to test this last 
week
This really is a minor comment ... can be addressed subsequently

On 2/24/2026 6:12 PM, Jamin Lin wrote:
> Adds a simple i3c device to be used for testing in lieu of a real
> device.
> 
> The mock target supports the following features:
> - A buffer that users can read and write to.
> - CCC support for commonly used CCCs when probing devices on an I3C bus.
> - IBI sending upon receiving a user-defined byte.
> 
> Signed-off-by: Joe Komlodi <[email protected]>
> Reviewed-by: Titus Rwantare <[email protected]>
> Reviewed-by: Patrick Venture <[email protected]>
> Reviewed-by: Jamin Lin <[email protected]>
> Signed-off-by: Jamin Lin <[email protected]>
> ---
>  include/hw/i3c/mock-i3c-target.h |  52 ++++++
>  hw/i3c/mock-i3c-target.c         | 298 +++++++++++++++++++++++++++++++
>  hw/i3c/Kconfig                   |  10 ++
>  hw/i3c/meson.build               |   1 +
>  hw/i3c/trace-events              |  10 ++
>  5 files changed, 371 insertions(+)
>  create mode 100644 include/hw/i3c/mock-i3c-target.h
>  create mode 100644 hw/i3c/mock-i3c-target.c
> 
> diff --git a/include/hw/i3c/mock-i3c-target.h 
> b/include/hw/i3c/mock-i3c-target.h
> new file mode 100644

...

> +static int mock_i3c_target_tx(I3CTarget *i3c, const uint8_t *data,
> +                              uint32_t num_to_send, uint32_t *num_sent)
> +{
> +    MockI3cTargetState *s = MOCK_I3C_TARGET(i3c);
> +    int ret;
> +    uint32_t to_write;
> +
> +    if (s->cfg.ibi_magic && num_to_send == 1 && s->cfg.ibi_magic == *data) {
> +        mock_i3c_target_ibi_timer_start(s);
> +        return 0;
> +    }
> +
> +    /* Bounds check. */
> +    if (num_to_send + s->p_buf > s->cfg.buf_size) {
> +        to_write = s->cfg.buf_size - s->p_buf;
> +        ret = -1;
> +    } else {
> +        to_write = num_to_send;
> +        ret = 0;
> +    }
> +    for (uint32_t i = 0; i < to_write; i++) {
> +        trace_mock_i3c_target_tx(data[i]);
> +        s->buf[s->p_buf] = data[i];
> +        s->p_buf++;
> +    }


num_sent is never updated prior to return, so the traces (from caller i3c_send) 
looked a bit confusing

<snip>
mock_i3c_target_tx I3C mock target write 0x12
i3c_send I3C send 0/1 bytes, ack=1   ---------------------> instead of 1/1 bytes
mock_i3c_target_tx I3C mock target write 0x34
i3c_send I3C send 0/1 bytes, ack=1
</snip>

Something like below is needed
+ *num_sent = to_write 
(might also needed in the ibi magic path above)


> +    return ret;
> +}
> +

Thanks
Jithu


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