scsi: NCR5380: Add disconnect_mask module parameter

Add a module parameter to inhibit disconnect/reselect for individual
targets. This gains compatibility with Aztec PowerMonster SCSI/SATA
adapters with buggy firmware. (No fix is available from the vendor.)

Apparently these adapters pass-through the product/vendor of the attached
SATA device. Since they can't be identified from the response to an INQUIRY
command, a device blacklist flag won't work.

Cc: Michael Schmitz <schmitzmic@gmail.com>
Link: https://lore.kernel.org/r/993b17545990f31f9fa5a98202b51102a68e7594.1573875417.git.fthain@telegraphics.com.au
Reviewed-and-tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/NCR5380.c

@@ -129,6 +129,9 @@
 #define NCR5380_release_dma_irq(x)
 #endif
 
+static unsigned int disconnect_mask = ~0;
+module_param(disconnect_mask, int, 0444);
+
 static int do_abort(struct Scsi_Host *);
 static void do_reset(struct Scsi_Host *);
 static void bus_reset_cleanup(struct Scsi_Host *);
@@ -967,7 +970,8 @@ static bool NCR5380_select(struct Scsi_Host *instance, struct scsi_cmnd *cmd)
 	int err;
 	bool ret = true;
 	bool can_disconnect = instance->irq != NO_IRQ &&
-			      cmd->cmnd[0] != REQUEST_SENSE;
+			      cmd->cmnd[0] != REQUEST_SENSE &&
+			      (disconnect_mask & BIT(scmd_id(cmd)));
 
 	NCR5380_dprint(NDEBUG_ARBITRATION, instance);
 	dsprintk(NDEBUG_ARBITRATION, instance, "starting arbitration, id = %d\n",