[SCSI] retry with missing data for INQUIRY

This patch changes scsi_probe_lun() to retry INQUIRY if the device has
not actually sent back any INQUIRY data,

This enables the Thecus N2050 storage device to work better. The
firmware on that device starts up strangely; it sends no data in
response to the initial INQUIRY, and it sends the INQUIRY information
in response to the followup REQUEST SENSE. But after that it works
better, so retrying the INQUIRY is enough to get it going.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/scsi_scan.c

@@ -573,6 +573,8 @@ static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
 
 	/* Each pass gets up to three chances to ignore Unit Attention */
 	for (count = 0; count < 3; ++count) {
+		int resid;
+
 		memset(scsi_cmd, 0, 6);
 		scsi_cmd[0] = INQUIRY;
 		scsi_cmd[4] = (unsigned char) try_inquiry_len;
@@ -582,7 +584,7 @@ static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
 		result = scsi_execute_req(sdev,  scsi_cmd, DMA_FROM_DEVICE,
 					  inq_result, try_inquiry_len, &sshdr,
 					  HZ / 2 + HZ * scsi_inq_timeout, 3,
-					  NULL);
+					  &resid);
 
 		SCSI_LOG_SCAN_BUS(3, printk(KERN_INFO "scsi scan: INQUIRY %s "
 				"with code 0x%x\n",
@@ -603,6 +605,14 @@ static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
 				    (sshdr.ascq == 0))
 					continue;
 			}
+		} else {
+			/*
+			 * if nothing was transferred, we try
+			 * again. It's a workaround for some USB
+			 * devices.
+			 */
+			if (resid == try_inquiry_len)
+				continue;
 		}
 		break;
 	}