[PATCH] libata: fallback to the other IDENTIFY on device error

[Tejun Heo <htejun@gmail.com>]

It seems the world isn't as frank as we thought and some devices lie
about who they are.  Fallback to the other IDENTIFY if IDENTIFY fails
with device error.  As this is the strategy used by IDE for a long
time, it shouldn't cause too much problem.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: William Thompson <wt@electro-mechanical.com>
---
Willam, please verify this fixes your problem.  Jeff, after all, we
seem to need this.  :-(

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index ca67484..f543109 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1652,7 +1652,7 @@ int ata_dev_read_id(struct ata_device *d
 	struct ata_taskfile tf;
 	unsigned int err_mask = 0;
 	const char *reason;
-	int tried_spinup = 0;
+	int may_fallback = 1, tried_spinup = 0;
 	int rc;
 
 	if (ata_msg_ctl(ap))
@@ -1696,11 +1696,30 @@ int ata_dev_read_id(struct ata_device *d
 			return -ENOENT;
 		}
 
+		if (may_fallback && (err_mask == AC_ERR_DEV)) {
+			may_fallback = 0;
+
+			/* Device or controller might have reported
+			 * the wrong device class.  Give a shot at then
+			 * other IDENTIFY
+			 */
+			if (class == ATA_DEV_ATA)
+				class = ATA_DEV_ATAPI;
+			else
+				class = ATA_DEV_ATA;
+			goto retry;
+		}
+
 		rc = -EIO;
 		reason = "I/O error";
 		goto err_out;
 	}
 
+	/* Falling back doesn't make sense if ID data was read
+	 * successfully at least once.
+	 */
+	may_fallback = 0;
+
 	swap_buf_le16(id, ATA_ID_WORDS);
 
 	/* sanity check */