Re: Interoperability problem with Quantum CD72SH SATA tape drive and libata

[Tejun Heo <tj@kernel.org>]

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John Clark wrote:
>> We can create a HORKAGE for it.  Can you please post the result of
>> "hdparm -I" of the device?
>>
>>   
> Tejun,
> 
> Here it is:
> 
> /dev/nst0:
> 
> ATAPI Sequential-access device, with removable media
>    Model Number:       QUANTUM DAT    DAT72-000

Can you please test the attached patch?

Alan, John Clark is reporting that the above tape drive chokes on odd
byte PIO transfer, so the default condition check (qc->nbytes & 15) in
atapi_check_dma() breaks the SATA tape drive, so there's always one
which breaks the other way around.  :-(

For the time being, I think the horkage should do.  I was wondering
whether you still think we should lift the default mod16 check in
atapi_check_dma().

Thanks.

-- 
tejun

[-- Attachment #2: horkage_atapi_mod16_dma.patch --]
[-- Type: text/x-patch, Size: 1384 bytes --]

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 1ee9499..e97afce 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4023,6 +4023,7 @@ static const struct ata_blacklist_entry ata_device_blacklist [] = {
 
 	/* Weird ATAPI devices */
 	{ "TORiSAN DVD-ROM DRD-N216", NULL,	ATA_HORKAGE_MAX_SEC_128 },
+	{ "QUANTUM DAT    DAT72-000", NULL,	ATA_HORKAGE_ATAPI_MOD16_DMA },
 
 	/* Devices we expect to fail diagnostics */
 
@@ -4436,7 +4437,8 @@ int atapi_check_dma(struct ata_queued_cmd *qc)
 	/* Don't allow DMA if it isn't multiple of 16 bytes.  Quite a
 	 * few ATAPI devices choke on such DMA requests.
 	 */
-	if (unlikely(qc->nbytes & 15))
+	if (!(qc->dev->horkage & ATA_HORKAGE_ATAPI_MOD16_DMA) &&
+	    unlikely(qc->nbytes & 15))
 		return 1;
 
 	if (ap->ops->check_atapi_dma)
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 8bb81d0..9d903b3 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -371,6 +371,8 @@ enum {
 	ATA_HORKAGE_IPM		= (1 << 7),	/* Link PM problems */
 	ATA_HORKAGE_IVB		= (1 << 8),	/* cbl det validity bit bugs */
 	ATA_HORKAGE_STUCK_ERR	= (1 << 9),	/* stuck ERR on next PACKET */
+	ATA_HORKAGE_ATAPI_MOD16_DMA = (1 << 10), /* use ATAPI DMA for commands
+						    not multiple of 16 bytes */
 
 	 /* DMA mask for user DMA control: User visible values; DO NOT
 	    renumber */