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libata: increase 128 KB / cmd limit for ATAPI tape drives 

Commands sent to ATAPI tape drives via the SCSI generic (sg) driver are
limited in the amount of data that they can transfer by the max_sectors
value.  The max_sectors value is currently calculated according to the
command set for disk drives, which doesn't apply to tape drives.  The
default max_sectors value of 256 limits ATAPI tape drive commands to
128 KB.  This patch against 2.6.24-rc1 increases the max_sectors value
for tape drives to 65535, which permits tape drive commands to transfer
just under 32 MB.

Tested with a SuperMicro PDSME motherboard, AHCI, and a Sony SDX-570V
SATA tape drive.

Note that some of the chipset drivers also set their own max_sectors
value, which may override the value set in libata-core.  I don't have
any of these chipsets to test, so I didn't go messing with them.  Also,
ATAPI devices other than tape drives may benefit from similar changes,
but I have only tape drives and disk drives to test.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This commit is contained in:
Tony Battersby 2007-10-30 11:44:35 -04:00 committed by Jeff Garzik
parent 03116d67e0
commit f8d8e5799b
2 changed files with 10 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
drivers/ata/libata-core.c
View File

@ -2304,6 +2304,10 @@ int ata_dev_configure(struct ata_device *dev)
dev->max_sectors = ATA_MAX_SECTORS;
}
if ((dev->class == ATA_DEV_ATAPI) &&
(atapi_command_packet_set(id) == TYPE_TAPE))
dev->max_sectors = ATA_MAX_SECTORS_TAPE;
if (dev->horkage & ATA_HORKAGE_MAX_SEC_128)
dev->max_sectors = min_t(unsigned int, ATA_MAX_SECTORS_128,
dev->max_sectors);

6
include/linux/ata.h
View File

@ -43,6 +43,7 @@ enum {
ATA_MAX_SECTORS_128 = 128,
ATA_MAX_SECTORS = 256,
ATA_MAX_SECTORS_LBA48 = 65535,/* TODO: 65536? */
ATA_MAX_SECTORS_TAPE = 65535,
ATA_ID_WORDS = 256,
ATA_ID_SERNO = 10,
@ -544,6 +545,11 @@ static inline int atapi_cdb_len(const u16 *dev_id)
}
}
static inline int atapi_command_packet_set(const u16 *dev_id)
{
return (dev_id[0] >> 8) & 0x1f;
}
static inline int is_atapi_taskfile(const struct ata_taskfile *tf)
{
return (tf->protocol == ATA_PROT_ATAPI) ||