[PATCH] libata handle the case when device returns/needs extra data

PATCH 2/2:  handle the case when device returns/needs extra data

Description:
   Sometimes the device returns/needs extra data than expected.

Changes:
   Modify __atapi_pio_bytes() to handle the case where device returns/needs extra data.
     - for read case, discard trailing data from the device
     - for write case, padding zero data to the device

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>

1 files changed, 25 insertions, 3 deletions

diff --git a/drivers/scsi/libata-core.c b/drivers/scsi/libata-core.c
index 8f6e536d8924..9add4c521b6b 100644
--- a/drivers/scsi/libata-core.c
+++ b/drivers/scsi/libata-core.c
@@ -2697,10 +2697,33 @@ static void __atapi_pio_bytes(struct ata_queued_cmd *qc, unsigned int bytes)
         unsigned char *buf;
         unsigned int offset, count;
 
-        if (qc->curbytes == qc->nbytes - bytes)
+        if (qc->curbytes + bytes >= qc->nbytes)
                 ap->pio_task_state = PIO_ST_LAST;
 
 next_sg:
+        if (unlikely(qc->cursg >= qc->n_elem)) {
+                /* 
+                 * The end of qc->sg is reached and the device expects
+                 * more data to transfer. In order not to overrun qc->sg
+                 * and fulfill length specified in the byte count register,
+                 *    - for read case, discard trailing data from the device
+                 *    - for write case, padding zero data to the device
+                 */
+                u16 pad_buf[1] = { 0 };
+                unsigned int words = bytes >> 1;
+                unsigned int i;
+
+                if (words) /* warning if bytes > 1 */
+                        printk(KERN_WARNING "ata%u: %u bytes trailing data\n", 
+                               ap->id, bytes);
+
+                for (i = 0; i < words; i++)
+                        ata_data_xfer(ap, (unsigned char*)pad_buf, 2, do_write);
+
+                ap->pio_task_state = PIO_ST_LAST;
+                return;
+        }
+
         sg = &qc->sg[qc->cursg];
 
         page = sg->page;
@@ -2734,9 +2757,8 @@ next_sg:
 
         kunmap(page);
 
-        if (bytes) {
+        if (bytes)
                 goto next_sg;
-        }
 }
 
 /**