Re: [PATCH] i3c: mipi-i3c-hci: fix IBI payload length calculation for final status

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

On 31/03/2026 13:27, Billy Tsai wrote:
> In DMA mode, the IBI status descriptor encodes the payload using
> CHUNKS (number of chunks) and DATA_LENGTH (valid bytes in the last
> chunk). All preceding chunks are implicitly full-sized.
> 
> The current code accumulates full chunk sizes for non-final status
> descriptors, but for the final status descriptor it only adds
> DATA_LENGTH. This ignores the contribution of the preceding full
> chunks described by the same final status entry.
> 
> As a result, the computed IBI payload length is truncated whenever
> the final status spans multiple chunks. For example, with a chunk
> size of 4 bytes, CHUNKS=2 and DATA_LENGTH=1 should result in a total
> payload size of 5 bytes, but the current code reports only 1 byte.
> 
> Fix the calculation by adding the size of (CHUNKS - 1) full chunks
> plus DATA_LENGTH for the last chunk.
> 
> Fixes: 9ad9a52cce28 ("i3c/master: introduce the mipi-i3c-hci driver")
> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
> ---
>  drivers/i3c/master/mipi-i3c-hci/dma.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/i3c/master/mipi-i3c-hci/dma.c b/drivers/i3c/master/mipi-i3c-hci/dma.c
> index b903a2da1fd1..f4c76f168276 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/dma.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
> @@ -721,6 +721,7 @@ static void hci_dma_process_ibi(struct i3c_hci *hci, struct hci_rh_data *rh)
>  		if (!(ibi_status & IBI_LAST_STATUS)) {
>  			ibi_size += chunks * rh->ibi_chunk_sz;
>  		} else {
> +			ibi_size += (chunks - 1) * rh->ibi_chunk_sz;

That assumes chunks is not 0.  It would be better to
defend against that possibility i.e.

			if (chunks) {
				ibi_size += (chunks - 1) * rh->ibi_chunk_sz;
				ibi_size += FIELD_GET(IBI_DATA_LENGTH, ibi_status);
			}

>  			ibi_size += FIELD_GET(IBI_DATA_LENGTH, ibi_status);
>  			last_ptr = ptr;
>  			break;
> 
> ---
> base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
> change-id: 20260331-i3c-hci-dma-3aae908b4e8e
> 
> Best regards,