scsi: atari_scsi: Reset DMA during bus reset only under ST-DMA lock

The atari_scsi driver should not access Falcon DMA chip registers unless
it has acquired exclusive access to that chip. If the driver doesn't
have exclusive access then there's no need for a DMA reset as there are
no scsi commands in progress.
Signed-off-by: NFinn Thain <fthain@telegraphics.com.au>
Tested-by: NOndrej Zary <linux@rainbow-software.org>
Tested-by: NMichael Schmitz <schmitzmic@gmail.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/atari_scsi.c

@@ -682,7 +682,8 @@ static int atari_scsi_bus_reset(struct scsi_cmnd *cmd)
 	if (IS_A_TT()) {
 		tt_scsi_dma.dma_ctrl = 0;
 	} else {
-		st_dma.dma_mode_status = 0x90;
+		if (stdma_is_locked_by(scsi_falcon_intr))
+			st_dma.dma_mode_status = 0x90;
 		atari_dma_active = 0;
 		atari_dma_orig_addr = NULL;
 	}