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@xxxxxxxxxxxxxxx>
---
diff -urpN linux-2.6.24-rc1-vanilla/drivers/ata/libata-core.c linux-2.6.24-rc1/drivers/ata/libata-core.c
--- linux-2.6.24-rc1-vanilla/drivers/ata/libata-core.c 2007-10-30 09:21:38.000000000 -0400
+++ linux-2.6.24-rc1/drivers/ata/libata-core.c 2007-10-30 11:35:57.000000000 -0400
@@ -2126,6 +2126,10 @@ int ata_dev_configure(struct ata_device
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);
diff -urpN linux-2.6.24-rc1-vanilla/include/linux/ata.h linux-2.6.24-rc1/include/linux/ata.h
--- linux-2.6.24-rc1-vanilla/include/linux/ata.h 2007-10-30 09:21:54.000000000 -0400
+++ linux-2.6.24-rc1/include/linux/ata.h 2007-10-30 10:30:59.000000000 -0400
@@ -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,
@@ -522,6 +523,11 @@ static inline int atapi_cdb_len(const u1
}
}
+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) ||
-
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