[bug report] wifi: ath12k: confusing alignment

[Dan Carpenter]

Hello Kalle Valo,

The patch d889913205cf: "wifi: ath12k: driver for Qualcomm Wi-Fi 7
devices" from Nov 28, 2022, leads to the following Smatch static
checker warning:

drivers/net/wireless/ath/ath12k/dbring.c:94 ath12k_dbring_fill_bufs() warn: assigning negative subtract to bytes: 'size = 8 + ring->buf_sz + align - 1'
drivers/net/wireless/ath/ath12k/dbring.c:288 ath12k_dbring_buffer_release_event() warn: assigning negative subtract to bytes: 'size = 8 + ring->buf_sz + ring->buf_align - 1'

drivers/net/wireless/ath/ath12k/dbring.c
    75 static int ath12k_dbring_fill_bufs(struct ath12k *ar,
    76                                    struct ath12k_dbring *ring,
    77                                    gfp_t gfp)
    78 {
    79         struct ath12k_dbring_element *buff;
    80         struct hal_srng *srng;
    81         struct ath12k_base *ab = ar->ab;
    82         int num_remain, req_entries, num_free;
    83         u32 align;
    84         int size, ret;
    85 
    86         srng = &ab->hal.srng_list[ring->refill_srng.ring_id];
    87 
    88         spin_lock_bh(&srng->lock);
    89 
    90         num_free = ath12k_hal_srng_src_num_free(ab, srng, true);
    91         req_entries = min(num_free, ring->bufs_max);
    92         num_remain = req_entries;
    93         align = ring->buf_align;
--> 94         size = sizeof(*buff) + ring->buf_sz + align - 1;

Where does this - 1 come from?  I feel like this should be:

	size = sizeof(*buff) + ALIGN(ring->buf_sz, ring->buf_align);

    95 
    96         while (num_remain > 0) {
    97                 buff = kzalloc(size, gfp);
    98                 if (!buff)
    99                         break;
    100 
    101                 ret = ath12k_dbring_bufs_replenish(ar, ring, buff, gfp);
    102                 if (ret) {
    103                         ath12k_warn(ab, "failed to replenish db ring num_remain %d req_ent %d\n",
    104                                     num_remain, req_entries);
    105                         kfree(buff);
    106                         break;
    107                 }
    108                 num_remain--;
    109         }
    110 
    111         spin_unlock_bh(&srng->lock);
    112 
    113         return num_remain;
    114 }

regards,
dan carpenter