Reallocation of DMA Resources for Data Transfer

For a previously allocated packet with data remaining to be transferred, the tran_init_pkt(9E) entry point must reallocate DMA resources when the following conditions apply:

• Partial DMA resources have already been allocated.

• A non-zero pkt_resid was returned in the previous call to tran_init_pkt(9E).

• bp is not null.

• bp->b_bcount is not zero.

When reallocating DMA resources to the next portion of the transfer, tran_init_pkt(9E) must return the amount of DMA resources not allocated for this transfer in the field pkt_resid.

If an error occurs while attempting to move DMA resources, tran_init_pkt(9E) must not free the scsi_pkt(9S). The target driver in this case is responsible for freeing the packet.

If the callback parameter is NULL_FUNC, the tran_init_pkt(9E) entry point must not sleep or call any function that might sleep. If the callback parameter is SLEEP_FUNC and resources are not immediately available, the tran_init_pkt(9E) entry point should sleep. Unless the request is impossible to satisfy, tran_init_pkt() should sleep until resources become available.

Example 18–4 DMA Resource Reallocation for HBA Drivers

static int
isp_i_dma_move(
    struct isp         *isp,
    struct scsi_pkt    *pkt,
    struct buf         *bp)
{
    struct isp_cmd     *sp  = (struct isp_cmd *)pkt->pkt_ha_private;
    int                i;

    ASSERT(sp->cmd_flags & CFLAG_COMPLETED);
    sp->cmd_flags &= ~CFLAG_COMPLETED;
    /*
     * If there are no more cookies remaining in this window,
     * must move to the next window first.
     */
    if (sp->cmd_cookie == sp->cmd_ncookies) {
        /*
         * For small pkts, leave things where they are
         */
        if (sp->cmd_curwin == sp->cmd_nwin && sp->cmd_nwin == 1)
            return (1);
        /*
         * At last window, cannot move
         */
        if (++sp->cmd_curwin >= sp->cmd_nwin)
            return (0);
        if (ddi_dma_getwin(sp->cmd_dmahandle, sp->cmd_curwin,
          &sp->cmd_dma_offset, &sp->cmd_dma_len,
          &sp->cmd_dmacookies[0], &sp->cmd_ncookies) == DDI_FAILURE)
            return (0);
        sp->cmd_cookie = 0;
    } else {
        /*
         * Still more cookies in this window - get the next one
         */
        ddi_dma_nextcookie(sp->cmd_dmahandle, &sp->cmd_dmacookies[0]);
    }
    /*
     * Get remaining cookies in this window, up to our maximum
     */
    i = 0;
    for (;;) {
        sp->cmd_dmacount += sp->cmd_dmacookies[i++].dmac_size;
        sp->cmd_cookie++;
        if (i == ISP_NDATASEGS || sp->cmd_cookie == sp->cmd_ncookies)
            break;
        ddi_dma_nextcookie(sp->cmd_dmahandle, &sp->cmd_dmacookies[i]);
    }
    sp->cmd_cookiecnt = i;
    pkt->pkt_resid = bp->b_bcount - sp->cmd_dmacount;
    return (1);
}