As I've mentioned in the comment/message, there is no ATA command
needed to be sent to the device, since it only toggles a bit in
dev->flags. See that there is no ata_taskfile constructed in
ata_mselect_control().

On 22 July 2016 at 05:26, Tejun Heo [off-list ref] wrote:

On Fri, Jul 22, 2016 at 02:41:54AM +0800, tom.ty89@gmail.com wrote:

quoted

@@ -3854,6 +3852,8 @@ static unsigned int ata_scsi_mode_select_xlat(struct ata_queued_cmd *qc)
              if (ata_mselect_control(qc, p, pg_len, &fp) < 0) {
                      fp += hdr_len + bd_len;
                      goto invalid_param;
+             } else {
+                     goto skip; /* No ATA command to send */

Hmmm... I'm a bit confused.  Why is mselect_control path different
from mselect_caching in terms of qc handling?

Thanks.

--
tejun