linux-kernel - Re: [PATCH] sata_nv: don't use legacy DMA in ADMA mode (v2)

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Date:	Sat, 24 Nov 2007 14:19:38 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Robert Hancock <hancockr@...w.ca>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	ide <linux-ide@...r.kernel.org>, Jeff Garzik <jeff@...zik.org>
Subject: Re: [PATCH] sata_nv: don't use legacy DMA in ADMA mode (v2)

Tejun Heo wrote:
> Robert Hancock wrote:
>> We need to run any DMA command with result taskfile requested in ADMA mode
>> when the port is in ADMA mode, otherwise it may try to use the legacy DMA engine
>> in ADMA mode which is not allowed. Enforce this with BUG_ON() since data
>> corruption could potentially result if this happened. Also WARN_ON() if we try
>> and send result taskfile commands while NCQ commands are still active, since the
>> hardware doesn't allow this.
>>
>> Signed-off-by: Robert Hancock <hancockr@...w.ca>
>>
>> @@ -1425,9 +1427,17 @@
>> +	/* We can't handle result taskfile with NCQ commands active, since
>> +	   retrieving the taskfile switches us out of ADMA mode and would abort
>> +	   existing commands. */
>> +	WARN_ON((qc->flags & ATA_QCFLAG_RESULT_TF) &&
>> +		(qc->ap->qc_allocated & ~(1 << qc->tag)));
> 
> I owe an apology here.  ap->qc_allocated & ~(1 << qc->tag) test isn't
> correct.  Sorry.  qc deferring happens after qc is allocated so the
> condition can trigger (although it should be rare) even when nothing is
> going wrong, so I guess it should be WARN_ON((qc->flags &
> ATA_QCFLAG_RESULT_TF) && link->sactive).

Or, just make the assumption clear by not allowing NCQ w/ RESULT_TF at all.

	if (unlikely(qc->tf.protocol == ATA_PROT_NCQ &&
		     (qc->flags & ATA_QCFLAG_RESULT_TF)) {
		ata_dev_printk(qc->dev, KERN_ERR,
			       "NCQ w/ RESULT_TF not allowed\n");
		return AC_ERR_SYSTEM;
	}

Thanks.

-- 
tejun
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