Writing Device Drivers

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 pkt.

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 until resources are available, unless the request is impossible to satisfy.

Example 15-4 HBA Driver DMA Resource Reallocation

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);
}

`tran_destroy_pkt()` Entry Point

The tran_destroy_pkt(9E) entry point is the HBA driver function that deallocates scsi_pkt(9S) structures. The tran_destroy_pkt() entry point is called when the target driver calls scsi_destroy_pkt(9F).

Thetran_destroy_pkt() entry point must free any DMA resources allocated for the packet. Freeing the DMA resources causes an implicit DMA synchronization if any cached data remained after the completion of the transfer. The tran_destroy_pkt() entry point frees the SCSI packet itself by calling scsi_hba_pkt_free(9F).

Example 15-5 HBA Driver tran_destroy_pkt(9E) Entry Point

static void
isp_scsi_destroy_pkt(
    struct scsi_address    *ap,
    struct scsi_pkt        *pkt)
{
    struct isp_cmd *sp = (struct isp_cmd *)pkt->pkt_ha_private;

    /*
     * Free the DMA, if any
     */
    if (sp->cmd_flags & CFLAG_DMAVALID) {
        sp->cmd_flags &= ~CFLAG_DMAVALID;
        (void) ddi_dma_unbind_handle(sp->cmd_dmahandle);
        ddi_dma_free_handle(&sp->cmd_dmahandle);
        sp->cmd_dmahandle = NULL;
    }
    /*
     * Free the pkt
     */
    scsi_hba_pkt_free(ap, pkt);
}


15. SCSI Host Bus Adapter Drivers SCSA HBA Entry Points Resource Allocation Allocation of DMA Resources

Reallocation of DMA Resources for Data Transfer

tran_destroy_pkt() Entry Point

`tran_destroy_pkt()` Entry Point