diff options
| -rw-r--r-- | drivers/ata/libata-scsi.c | 35 |
1 files changed, 32 insertions, 3 deletions
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c index a45f6ac3b24..a883bb03d4c 100644 --- a/drivers/ata/libata-scsi.c +++ b/drivers/ata/libata-scsi.c @@ -2485,11 +2485,40 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc) if (!using_pio && ata_check_atapi_dma(qc)) using_pio = 1; - /* Some controller variants snoop this value for Packet transfers - to do state machine and FIFO management. Thus we want to set it - properly, and for DMA where it is effectively meaningless */ + /* Some controller variants snoop this value for Packet + * transfers to do state machine and FIFO management. Thus we + * want to set it properly, and for DMA where it is + * effectively meaningless. + */ nbytes = min(qc->nbytes, (unsigned int)63 * 1024); + /* Most ATAPI devices which honor transfer chunk size don't + * behave according to the spec when odd chunk size which + * matches the transfer length is specified. If the number of + * bytes to transfer is 2n+1. According to the spec, what + * should happen is to indicate that 2n+1 is going to be + * transferred and transfer 2n+2 bytes where the last byte is + * padding. + * + * In practice, this doesn't happen. ATAPI devices first + * indicate and transfer 2n bytes and then indicate and + * transfer 2 bytes where the last byte is padding. + * + * This inconsistency confuses several controllers which + * perform PIO using DMA such as Intel AHCIs and sil3124/32. + * These controllers use actual number of transferred bytes to + * update DMA poitner and transfer of 4n+2 bytes make those + * controller push DMA pointer by 4n+4 bytes because SATA data + * FISes are aligned to 4 bytes. This causes data corruption + * and buffer overrun. + * + * Always setting nbytes to even number solves this problem + * because then ATAPI devices don't have to split data at 2n + * boundaries. + */ + if (nbytes & 0x1) + nbytes++; + qc->tf.lbam = (nbytes & 0xFF); qc->tf.lbah = (nbytes >> 8); |