libata: Expose TRIM capability in sysfs

Create a sysfs "trim" attribute for each ata_device that displays
whether DSM TRIM is "unsupported", "unqueued", "forced_unqueued"
(blacklisted) or "queued".

Signed-off-by: Martin K. Petersen <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

Documentation/ABI/testing/sysfs-ata

···
 	130:	SATA_PMP_GSCR_SII_GPIO
 	Only valid if the device is a PM.
 
+trim
+
+	Shows the DSM TRIM mode currently used by the device. Valid
+	values are:
+	unsupported:		Drive does not support DSM TRIM
+	unqueued:		Drive supports unqueued DSM TRIM only
+	queued:			Drive supports queued DSM TRIM
+	forced_unqueued:	Drive's unqueued DSM support is known to be
+				buggy and only unqueued TRIM commands
+				are sent
+
 spdn_cnt
 
 	Number of time libata decided to lower the speed of link due to errors.

drivers/ata/libata-transport.c

···
 
 static DEVICE_ATTR(gscr, S_IRUGO, show_ata_dev_gscr, NULL);
 
+static ssize_t
+show_ata_dev_trim(struct device *dev,
+		  struct device_attribute *attr, char *buf)
+{
+	struct ata_device *ata_dev = transport_class_to_dev(dev);
+	unsigned char *mode;
+
+	if (!ata_id_has_trim(ata_dev->id))
+		mode = "unsupported";
+	else if (ata_dev->horkage & ATA_HORKAGE_NO_NCQ_TRIM)
+			mode = "forced_unqueued";
+	else if (ata_fpdma_dsm_supported(ata_dev))
+		mode = "queued";
+	else
+		mode = "unqueued";
+
+	return snprintf(buf, 20, "%s\n", mode);
+}
+
+static DEVICE_ATTR(trim, S_IRUGO, show_ata_dev_trim, NULL);
+
 static DECLARE_TRANSPORT_CLASS(ata_dev_class,
 			       "ata_device", NULL, NULL, NULL);
 
···
 	SETUP_DEV_ATTRIBUTE(ering);
 	SETUP_DEV_ATTRIBUTE(id);
 	SETUP_DEV_ATTRIBUTE(gscr);
+	SETUP_DEV_ATTRIBUTE(trim);
 	BUG_ON(count > ATA_DEV_ATTRS);
 	i->dev_attrs[count] = NULL;