scsi: atari_scsi: Make device register accessors re-entrant

This patch fixes an old bug: accesses to device registers from the
interrupt handler (after reselection, DMA completion etc.) could mess
up a device register access elsewhere, if the latter takes place outside
of an irq lock (during selection etc.).

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/atari_scsi.c

@@ -670,14 +670,26 @@ static void atari_scsi_tt_reg_write(unsigned char reg, unsigned char value)
 
 static unsigned char atari_scsi_falcon_reg_read(unsigned char reg)
 {
-	dma_wd.dma_mode_status= (u_short)(0x88 + reg);
-	return (u_char)dma_wd.fdc_acces_seccount;
+	unsigned long flags;
+	unsigned char result;
+
+	reg += 0x88;
+	local_irq_save(flags);
+	dma_wd.dma_mode_status = (u_short)reg;
+	result = (u_char)dma_wd.fdc_acces_seccount;
+	local_irq_restore(flags);
+	return result;
 }
 
 static void atari_scsi_falcon_reg_write(unsigned char reg, unsigned char value)
 {
-	dma_wd.dma_mode_status = (u_short)(0x88 + reg);
+	unsigned long flags;
+
+	reg += 0x88;
+	local_irq_save(flags);
+	dma_wd.dma_mode_status = (u_short)reg;
 	dma_wd.fdc_acces_seccount = (u_short)value;
+	local_irq_restore(flags);
 }