Re: Comments - using the qc_defer hook for serializing controllers ?

[Tejun Heo <htejun@gmail.com>]

Alan Cox wrote:
> +/**
> + *	sl82c105_qc_defer	-	implement serialization
> + *	@qc: command
> + *
> + *	We must issue one command per host not per channel because
> + *	of the reset bug.
> + *
> + *	Q: is the scsi host lock sufficient ?
> + */
> +
> +static int sl82c105_qc_defer(struct ata_queued_cmd *qc)
> +{
> +	struct ata_host *host = qc->ap->host;
> +	int rc;
> +
> +	/* First apply the usual rules */	
> +	rc = ata_std_qc_defer(qc);
> +	if (rc != 0)
> +		return rc;
> +
> +	/* Now apply serialization rules. Only allow a command if the
> +	   other channel state machine is idle */
> +	if (host->port[0] != qc->ap && 
> +			host->port[0]->hsm_task_state != HSM_ST_IDLE)
> +		return	ATA_DEFER_PORT;
> +	if (host->port[1] != qc->ap && 
> +			host->port[1]->hsm_task_state != HSM_ST_IDLE)
> +		return	ATA_DEFER_PORT;
> +	return 0;
> +}

hsm_task_state is not necessarily protected by host lock.  I think
testing ap->qc_active would be better.

-- 
tejun