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path: root/drivers/ata/libata-scsi.c
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Diffstat (limited to 'drivers/ata/libata-scsi.c')
-rw-r--r--drivers/ata/libata-scsi.c35
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);