On 06/08/2015 05:30 PM, Matthew R. Ochs wrote:
> +
> +/**
> + * cxlflash_send_cmd() - sends an AFU command
> + * @afu: AFU associated with the host.
> + * @cmd: AFU command to send.
> + *
> + * Return:
> + * 0 on success
> + * -1 on failure
> + */
> +int cxlflash_send_cmd(struct afu *afu, struct afu_cmd *cmd)
> +{
> + int nretry = 0;
> + int rc = 0;
> + u64 room;
> + long newval;
> +
> + /*
> + * This routine is used by critical users such an AFU sync and to
> + * send a task management function (TMF). Thus we want to retry a
> + * bit before returning an error. To avoid the performance penalty
> + * of MMIO, we spread the update of 'room' over multiple commands.
> + */
> +retry:
> + newval = atomic64_dec_if_positive(&afu->room);
> + if (!newval) {
> + do {
> + room = readq_be(&afu->host_map->cmd_room);
> + atomic64_set(&afu->room, room);
> + if (room)
> + goto write_ioarrin;
> + } while (nretry++ < MC_ROOM_RETRY_CNT);
It looks like you removed the udelay here. Was that intentional?
> +
> + pr_err("%s: no cmd_room to send 0x%X\n",
> + __func__, cmd->rcb.cdb[0]);
> + rc = SCSI_MLQUEUE_HOST_BUSY;
If you actually get here, how do you get out of this state? Since now afu->room is
zero and anyone that comes through here will go to the else if leg.
> + goto out;
> + } else if (unlikely(newval < 0)) {
> + /* This should be rare. i.e. Only if two threads race and
> + * decrement before the MMIO read is done. In this case
> + * just benefit from the other thread having updated
> + * afu->room.
> + */
> + if (nretry++ < MC_ROOM_RETRY_CNT)
I'm guessing you'd want the udelay here as well.
> + goto retry;
> + else {
> + rc = SCSI_MLQUEUE_HOST_BUSY;
> + goto out;
> + }
> + }
> +
> +write_ioarrin:
> + writeq_be((u64)&cmd->rcb, &afu->host_map->ioarrin);
> +out:
> + pr_debug("%s: cmd=%p len=%d ea=%p rc=%d\n", __func__, cmd,
> + cmd->rcb.data_len, (void *)cmd->rcb.data_ea, rc);
> + return rc;
> +}
> +
--
Brian King
Power Linux I/O
IBM Linux Technology Center
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