[PATCH] libata: use qc->result_tf for temp taskfile storage

Use qc->result_tf for temp taskfile storage.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index aa38ed3e59a8..bf00d2b2e404 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -3865,10 +3865,16 @@ static void atapi_pio_bytes(struct ata_queued_cmd *qc)
         unsigned int ireason, bc_lo, bc_hi, bytes;
         int i_write, do_write = (qc->tf.flags & ATA_TFLAG_WRITE) ? 1 : 0;
 
-        ap->ops->tf_read(ap, &qc->tf);
-        ireason = qc->tf.nsect;
-        bc_lo = qc->tf.lbam;
-        bc_hi = qc->tf.lbah;
+        /* Abuse qc->result_tf for temp storage of intermediate TF
+         * here to save some kernel stack usage.
+         * For normal completion, qc->result_tf is not relevant. For
+         * error, qc->result_tf is later overwritten by ata_qc_complete().
+         * So, the correctness of qc->result_tf is not affected.
+         */
+        ap->ops->tf_read(ap, &qc->result_tf);
+        ireason = qc->result_tf.nsect;
+        bc_lo = qc->result_tf.lbam;
+        bc_hi = qc->result_tf.lbah;
         bytes = (bc_hi << 8) | bc_lo;
 
         /* shall be cleared to zero, indicating xfer of data */