mISDN: Implement MISDN_CTRL_RX_OFF for more drivers

MISDN_CTRL_RX_OFF is a meachanism to discard RX data in the driver if
the data is not needed by the application. It can be used when playing
mesages, but not recording or with unidirectional protocols.

Signed-off-by: Karsten Keil <kkeil@linux-pingi.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/mISDN/hwchannel.c b/drivers/isdn/mISDN/hwchannel.c
index e541b65..ef34fd4 100644
--- a/drivers/isdn/mISDN/hwchannel.c
+++ b/drivers/isdn/mISDN/hwchannel.c
@@ -142,6 +142,8 @@
 	test_and_clear_bit(FLG_ACTIVE, &ch->Flags);
 	test_and_clear_bit(FLG_FILLEMPTY, &ch->Flags);
 	test_and_clear_bit(FLG_TX_EMPTY, &ch->Flags);
+	test_and_clear_bit(FLG_RX_OFF, &ch->Flags);
+	ch->dropcnt = 0;
 	ch->minlen = ch->init_minlen;
 	ch->next_minlen = ch->init_minlen;
 	ch->maxlen = ch->init_maxlen;
@@ -167,7 +169,8 @@
 
 	switch (cq->op) {
 	case MISDN_CTRL_GETOP:
-		cq->op = MISDN_CTRL_RX_BUFFER | MISDN_CTRL_FILL_EMPTY;
+		cq->op = MISDN_CTRL_RX_BUFFER | MISDN_CTRL_FILL_EMPTY |
+			 MISDN_CTRL_RX_OFF;
 		break;
 	case MISDN_CTRL_FILL_EMPTY:
 		if (cq->p1) {
@@ -177,6 +180,15 @@
 			test_and_clear_bit(FLG_FILLEMPTY, &bch->Flags);
 		}
 		break;
+	case MISDN_CTRL_RX_OFF:
+		/* read back dropped byte count */
+		cq->p2 = bch->dropcnt;
+		if (cq->p1)
+			test_and_set_bit(FLG_RX_OFF, &bch->Flags);
+		else
+			test_and_clear_bit(FLG_RX_OFF, &bch->Flags);
+		bch->dropcnt = 0;
+		break;
 	case MISDN_CTRL_RX_BUFFER:
 		if (cq->p2 > MISDN_CTRL_RX_SIZE_IGNORE)
 			bch->next_maxlen = cq->p2;