[PATCH] Blacklist devices that falsely claim an echo buffer

A particular type of DVD is wrongly claiming to have an echo buffer
(but only if a DVD is inserted).  This confuses domain validation, so
only look for an echo buffer if the device supports ppr (this is all
SCSI3 and above devices plus LVD SCSI2 devices).
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/scsi_transport_spi.c

@@ -634,7 +634,11 @@ spi_dv_device_internal(struct scsi_request *sreq, u8 *buffer)
 	/* OK, now we have our initial speed set by the read only inquiry
 	 * test, now try an echo buffer test (if the device allows it) */
 
-	if ((len = spi_dv_device_get_echo_buffer(sreq, buffer)) == 0) {
+	len = 0;
+	if (sdev->ppr)
+		len = spi_dv_device_get_echo_buffer(sreq, buffer);
+
+	if (len == 0) {
 		SPI_PRINTK(sdev->sdev_target, KERN_INFO, "Domain Validation skipping write tests\n");
 		return;
 	}