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>

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 4dc6befa576078ca992090b67b215c3a558469a2..24b3bd63621fe20f4ec089373f42f277914f6a77 100644 (file)
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -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);

diff --git a/include/linux/ata.h b/include/linux/ata.h
index 128dc7ad49017c16446b8dfa6fd32d2df2dba8dd..61535e72834dcf79403a222c6875d95cafea619a 100644 (file)
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -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) ||