ata: expose ncq_enable_prio sysfs attribute only on NCQ capable hosts

There is no point in exposing ncq_enable_prio sysfs attribute for
devices on PATA and non-NCQ capable SATA hosts so:

* remove dev_attr_ncq_prio_enable from ata_common_sdev_attrs[]

* add ata_ncq_sdev_attrs[]

* update ATA_NCQ_SHT() macro to use ata_ncq_sdev_attrs[]

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/ata/libata-scsi.c

@@ -463,11 +463,17 @@ EXPORT_SYMBOL_GPL(dev_attr_sw_activity);
 
 struct device_attribute *ata_common_sdev_attrs[] = {
 	&dev_attr_unload_heads,
-	&dev_attr_ncq_prio_enable,
 	NULL
 };
 EXPORT_SYMBOL_GPL(ata_common_sdev_attrs);
 
+struct device_attribute *ata_ncq_sdev_attrs[] = {
+	&dev_attr_unload_heads,
+	&dev_attr_ncq_prio_enable,
+	NULL
+};
+EXPORT_SYMBOL_GPL(ata_ncq_sdev_attrs);
+
 /**
  *	ata_std_bios_param - generic bios head/sector/cylinder calculator used by sd.
  *	@sdev: SCSI device for which BIOS geometry is to be determined

include/linux/libata.h

@@ -1334,14 +1334,15 @@ extern int ata_link_nr_enabled(struct ata_link *link);
 extern const struct ata_port_operations ata_base_port_ops;
 extern const struct ata_port_operations sata_port_ops;
 extern struct device_attribute *ata_common_sdev_attrs[];
+extern struct device_attribute *ata_ncq_sdev_attrs[];
 
 /*
  * All sht initializers (BASE, PIO, BMDMA, NCQ) must be instantiated
  * by the edge drivers.  Because the 'module' field of sht must be the
  * edge driver's module reference, otherwise the driver can be unloaded
  * even if the scsi_device is being accessed.
  */
-#define ATA_BASE_SHT(drv_name)					\
+#define __ATA_BASE_SHT(drv_name)				\
 	.module			= THIS_MODULE,			\
 	.name			= drv_name,			\
 	.ioctl			= ata_scsi_ioctl,		\
@@ -1355,11 +1356,15 @@ extern struct device_attribute *ata_common_sdev_attrs[];
 	.slave_configure	= ata_scsi_slave_config,	\
 	.slave_destroy		= ata_scsi_slave_destroy,	\
 	.bios_param		= ata_std_bios_param,		\
-	.unlock_native_capacity	= ata_scsi_unlock_native_capacity, \
+	.unlock_native_capacity	= ata_scsi_unlock_native_capacity
+
+#define ATA_BASE_SHT(drv_name)					\
+	__ATA_BASE_SHT(drv_name),				\
 	.sdev_attrs		= ata_common_sdev_attrs
 
 #define ATA_NCQ_SHT(drv_name)					\
-	ATA_BASE_SHT(drv_name),					\
+	__ATA_BASE_SHT(drv_name),				\
+	.sdev_attrs		= ata_ncq_sdev_attrs,		\
 	.change_queue_depth	= ata_scsi_change_queue_depth
 
 /*