ncr5380: Fix pseudo DMA transfers on 53C400

Pseudo-DMA (PDMA) has been broken for ages, resulting in hangs on
53C400-based cards.

According to 53C400 datasheet, PDMA transfer length must be a multiple
of 128. Check if that's true and use PIO if it's not.

This makes PDMA work on 53C400 (Canon FG2-5202).
Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/g_NCR5380.c

@@ -702,6 +702,10 @@ static int generic_NCR5380_dma_xfer_len(struct scsi_cmnd *cmd)
 	    !(cmd->SCp.this_residual % transfersize))
 		transfersize = 32 * 1024;
 
+	/* 53C400 datasheet: non-modulo-128-byte transfers should use PIO */
+	if (transfersize % 128)
+		transfersize = 0;
+
 	return transfersize;
 }