libata: Media rotation rate and form factor heuristics

This patch provides new heuristics for parsing both the form factor and
media rotation rate ATA IDENFITY words.

The reported ATA version must be 7 or greater and the device must return
values defined as valid in the standard. Only then are the
characteristics reported to SCSI via the VPD B1 page.

This seems like a reasonable compromise to me considering that we have
been shipping several kernel releases that key off the rotation rate bit
without any version checking whatsoever. With no complaints so far.

Signed-off-by: Martin K. Petersen <[e-mail]>
Signed-off-by: Jeff Garzik <[e-mail]>

drivers/ata/libata-scsi.c

···
 
 static unsigned int ata_scsiop_inq_b1(struct ata_scsi_args *args, u8 *rbuf)
 {
+	int form_factor = ata_id_form_factor(args->id);
+	int media_rotation_rate = ata_id_rotation_rate(args->id);
+
 	rbuf[1] = 0xb1;
 	rbuf[3] = 0x3c;
-	if (ata_id_major_version(args->id) > 7) {
-		rbuf[4] = args->id[217] >> 8;
-		rbuf[5] = args->id[217];
-		rbuf[7] = args->id[168] & 0xf;
-	}
+	rbuf[4] = media_rotation_rate >> 8;
+	rbuf[5] = media_rotation_rate;
+	rbuf[7] = form_factor;
 
 	return 0;
 }

include/linux/ata.h

···
 	return 0;
 }
 
+static inline int ata_id_form_factor(const u16 *id)
+{
+	u16 val = id[168];
+
+	if (ata_id_major_version(id) < 7 || val == 0 || val == 0xffff)
+		return 0;
+
+	val &= 0xf;
+
+	if (val > 5)
+		return 0;
+
+	return val;
+}
+
+static inline int ata_id_rotation_rate(const u16 *id)
+{
+	u16 val = id[217];
+
+	if (ata_id_major_version(id) < 7 || val == 0 || val == 0xffff)
+		return 0;
+
+	if (val > 1 && val < 0x401)
+		return 0;
+
+	return val;
+}
+
 static inline int ata_id_has_trim(const u16 *id)
 {
 	if (ata_id_major_version(id) >= 7 &&