llc_conn_ac_inc_npta_value() and llc_conn_ac_inc_tx_win_size() clamp their counters to the maximum valid 7-bit value via (u8) ~LLC_2_SEQ_NBR_MODULO. LLC_2_SEQ_NBR_MODULO is defined as ((u8) 128) in include/net/llc_pdu.h, but the (u8) cast does not prevent integer promotion of the operand of ~: ~128 is computed as int (0xffffff7f), and the surrounding (u8) cast truncates back to 0x7f. The result is correct (127), but the implicit truncation is flagged by sparse: net/llc/llc_c_ac.c:1008:38: warning: cast truncates bits from constant value (ffffff7f becomes 7f) (and three more at lines 1009, 1099, 1100) Replace the (u8) ~LLC_2_SEQ_NBR_MODULO expression with LLC_2_SEQ_NBR_MODULO - 1, which evaluates to 127 directly and silences sparse. The same ~LLC_2_SEQ_NBR_MODULO pattern also appears in include/net/llc_pdu.h:148 as part of PDU_GET_NEXT_Vr, but there the result is immediately &-masked, so the int promotion is harmless and sparse does not flag it; it is left alone. This patch is the minimum diff to silence the warning. The counter-clamp idiom itself could be modernized to min_t(u8, ..., LLC_2_SEQ_NBR_MODULO - 1), but that is a separate cleanup left for another patch. No functional change. Signed-off-by: Avinash Duduskar --- Built with CONFIG_LLC2=m; full kernel build clean, sparse no longer warns on the touched lines. net/llc/llc_c_ac.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/llc/llc_c_ac.c b/net/llc/llc_c_ac.c index 0779daa8aa8f..ab86c720b3ec 100644 --- a/net/llc/llc_c_ac.c +++ b/net/llc/llc_c_ac.c @@ -1005,8 +1005,8 @@ static int llc_conn_ac_inc_npta_value(struct sock *sk, struct sk_buff *skb) llc->dec_step = 0; llc->dec_cntr = llc->inc_cntr = 2; ++llc->npta; - if (llc->npta > (u8) ~LLC_2_SEQ_NBR_MODULO) - llc->npta = (u8) ~LLC_2_SEQ_NBR_MODULO; + if (llc->npta > LLC_2_SEQ_NBR_MODULO - 1) + llc->npta = LLC_2_SEQ_NBR_MODULO - 1; } else --llc->inc_cntr; return 0; @@ -1096,8 +1096,8 @@ int llc_conn_ac_inc_tx_win_size(struct sock *sk, struct sk_buff *skb) struct llc_sock *llc = llc_sk(sk); llc->k += 1; - if (llc->k > (u8) ~LLC_2_SEQ_NBR_MODULO) - llc->k = (u8) ~LLC_2_SEQ_NBR_MODULO; + if (llc->k > LLC_2_SEQ_NBR_MODULO - 1) + llc->k = LLC_2_SEQ_NBR_MODULO - 1; return 0; } base-commit: 8ebd24a7822cbae25beeafba49b2159d6a68a5f2 -- 2.54.0