libata-pmp-prep: implement ATA_HORKAGE_SKIP_PM

Some pseudo devices fail PM commands unnecessarily aborting system
suspend.  Implement ATA_HORKAGE_SKIP_PM which makes libata skip PM
commands for these devices.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-scsi.c

@@ -944,6 +944,13 @@ static unsigned int ata_scsi_start_stop_xlat(struct ata_queued_cmd *qc)
 		goto invalid_fld;       /* LOEJ bit set not supported */
 	if (((cdb[4] >> 4) & 0xf) != 0)
 		goto invalid_fld;       /* power conditions not supported */
+
+	if (qc->dev->horkage & ATA_HORKAGE_SKIP_PM) {
+		/* the device lacks PM support, finish without doing anything */
+		scmd->result = SAM_STAT_GOOD;
+		return 1;
+	}
+
 	if (cdb[4] & 0x1) {
 		tf->nsect = 1;	/* 1 sector, lba=0 */
 

include/linux/libata.h

@@ -329,6 +329,7 @@ enum {
 	ATA_HORKAGE_NONCQ	= (1 << 2),	/* Don't use NCQ */
 	ATA_HORKAGE_MAX_SEC_128	= (1 << 3),	/* Limit max sects to 128 */
 	ATA_HORKAGE_BROKEN_HPA	= (1 << 4),	/* Broken HPA */
+	ATA_HORKAGE_SKIP_PM	= (1 << 5),	/* Skip PM operations */
 };
 
 enum hsm_task_states {